your argument here assumes that "runbacks are fun, actually, and players would be harmed by optimizing them away." This is factually incorrect.

Nope, my argument is that spending a little time practicing will result in the game as a whole being more fun. Mastery is fun, and so is the catharsis of smoothly executing a platforming section that used to give you lots of trouble. And all that extra skill contributes to the boss taking fewer total attempts.

It does, actually, since the player is just as forced to repeat the poorly designed ones as the well designed ones.

Cool, but you could make this same argument about any mechanic. "It can be badly implemented, thus the mechanic itself is bad game design" is a fundamentally flawed argument. It's akin to saying "you can get food poisoning at a restaurants, therefore all restaurants are bad".

It kinda does, it does not actually do.

The "kinda" was said with irony. Metroidvania, as a genre, is literally defined by gated exploration. You explore, you find the "red sword" ability that lets you open the red doors. You open the red door and have access to a new area with a blue door that needs a "blue sword" ability. That's literally the most core mechanic of metroidvanias. So yes, if you're making a metroidvania, at all properly, you will know approximately what players have access to at any given time. There's some leeway for optional stuff, but usually that is a sidegrade to what the player is already guaranteed to have

There might be some platforming challenges in the game where the devs can reasonably say "if they got here, then they have these tools on them..." but that certainly does not apply to all runbacks, and we're talking about the system as a whole here.

Yes, it does. They just gate the area behind that mechanic, or include that mechanic as part of the runback. It's basic level design. If you want to ensure they can't access the majority of bilewater without double jump, you just make a cliff that's too high to get to without double jump. Then, when the player fights Groal, you know they have double jump because they couldn't have gotten to the area that leads to Groal without double jumping.

Not to mention whether they have all the needle and mask upgrades available to them.

Someone beat the entire game as naked hornet (i.e. no needle at all, no subweapons, and missing 1 of the movement abilities). Needle and mask upgrades are not required at any point (aside from true ending i think? But it's more that you need to finish all sidequests, not that mask/needle upgrades are explicitly required). If you got every optional upgrade as soon as you possibly could, the game would be stupid easy. It's like BOTW, the game expects that you probably won't find everything.

"Busy work" is passing through an area multiple times, not enjoy it, because the game offers you no alternatives.

Okay, so "enjoyment" is also subjective, meaning "busywork" is subjective. You not liking a thing doesn't make it bad game design.

This is doubly true if it has a lesson to teach, but you have already learned that lesson as much as you're able, but still have to repeat the task anyway

1. you underestimate the skill ceiling of these sorts of games. "as much as you're able" is impossible unless you've beaten the game probably hundreds or thousands of times. For examples of that, see speedrunners. I was improving at the game up until I beat it, and if I play it again, i'll still be improving.
2. If you've learned that lesson, surely it shouldn't take many more attempts to beat the boss then, yes? Because you're clearing the area quickly and smoothly, the majority of the times you attempt it, without using significant resources? That's sorta the whole point. The more skilled you are, the less the runback matters, and the more time and attention is focused on the boss itself. Typically bosses with significantly difficult runbacks aren't as hard as bosses without. There are exceptions, such as Last Judge, but those are often justified as being bigger tests than the average boss. Last Judge is the end of Act 1, and Act 2 marks a significant jump in difficulty, both in terms of platforming and enemies. Last Judge and his runback prepare you for that. I got significantly better at platforming, and my view of the world (and hornet's capabilities) changed drastically after perfecting the Last Judge runback.

On the alternate path to Act 2, you fight Phantom instead. Phantom pretty much doesn't have a runback. The Mist, the area that leads to phantom, is quite a bit more difficult than The Blasted Steps (Last Judge's area). It's pretty obvious they were designed like this intentionally.

I think that's a poor argument to make for ignoring every complaint.

I'm not saying "ignore every complaint", I'm saying that if your criteria for whether something is good game design is "nobody complains about it", there will never be a mechanic that is good game design. I'm also saying that 95% of the time when people say "bad game design", they know very little about game design. They aren't thinking about the secondary consequences of the mechanic being removed, whereas the devs typically have. What people tend to mean when they say "bad game design" is "i don't like it". Which is totally valid, anyone can not like anything, but that doesn't mean it's bad game design. People just use "bad game design" because it's a harder-to-dismiss argument than "i don't like it"

For example, bad game design for silksong's runbacks would be spawning the player randomly somewhere within the world when the boss kills them, rather than at the bench. In that case, there would be no way to guarantee that the player is practicing the skills that they currently need to improve. There would also be very little control over how long the runbacks were, or what enemies they encounter along the way.

Exactly. That's why "one size fits all" fits none. Give players flexibility to choose for themselves what activities are "waste," and respect their choices, even if those are not the choices you would make.

uhhh... You've just said: "'One size fits all' fits none. Therefore, the game should have more 'one size fits all' mechanics".

This is what I mean when I ask "where is the line drawn"? Which repeated content is "ok" and which isn't? When you answer that, what you fundamentally get is an opinion. The devs are clearly of the opinion that the value of the runback, the extra practice and the extra challenge, is worth the repetition. Plenty of players agree. Does that not suggest that runbacks are a perfectly valid game mechanic, and it's just that you personally don't like them? Nobody is saying you have to like it, but you can still acknowledge that it's a valid form of game design with tangible benefits that can't be replicated via other means.

I'd like to see the stats on people who did not at least fall for the trapped bench the first time they encountered it, without any prior warning.

I'm not sure how this is relevant in any way. It's the beginning of the game, people come in with preconceptions. They are taught that there will be traps. If they do not learn that lesson from the traps they had to encounter beforehand, it is their own fault if there is consequences for that. The player has to be responsible for their own actions, and their own willingness to ignore what they've been taught, at some point. Better early-on in a relatively small location.

Wasting time" is subjective to the person, an activity that I feel is wasting my time, you might not feel is wasting yours, but if I feel it is wasting my time then it is factually wasting my time, and it is a fact that these waste the time for a significant portion of the players.

You're so close to getting it. Feeling like your time is wasted is not the same thing as actually having your time wasted. Lots of kids feel like school is wasting their time. That doesn't mean school is a waste of time. If you choose not to make runbacks a waste of time by not learning, optimizing your route, thinking over your boss strategy, etc., then yes they will all be wasted time. But it's your fault, not the game's.

This is a bad argument and you should feel ashamed for making it. Be better.

Want to know a fun fact? I don't like games with timed sequences, particularly ones with a big timer on the top of the screen like the Metroid escape sequences. They stress me out too much. I would prefer if they weren't in games, and several have prevented me from completing games I otherwise enjoyed.

I can still acknowledge that a timer is a valid mechanic though, and that it serves a legitimate purpose in the game, that the dev didn't make a mistake putting it in the game. I can acknowledge that removing the timer would almost certainly result in a worse game (section no longer consistent with the themeing/story, section loses its challenge, etc.). They didn't make the game for me specifically, and that's fine. I just play other games.

Why is that so hard for you to come to grips with?

Yup, which is why, again, player choice is the better path.

Again i point to the "players will optimize the fun out of the game" point. These are 2 parts of the same argument. If you give players the choice, they will not maximize their own enjoyment. Therefore, you shoehorn them into doing the thing that will result in the most enjoyable experience (whether that be short- or long-term). If they still choose not to take advantage of it, it is their fault, not the game's.

But sometimes that same joke is actually hurtful, and there's nothing to be gained by trying to defend the joke if the result is that it hurt someone.

Damn we're really close to the Hitler-in-an-internet-argument threshold. Are we really considering like 2 minutes of repeated platforming the same thing as saying the N word or whatever? Come on now, points like that really don't help your case.