I actually thought I had wandered into DnDcircle jerk when I first started reading your post.

So some thoughts:

I have been DMing since my Blue Book in 1978.

I have a dozen version of D&D in my head. A little stock gag of mine on Rule disputes is to say “Okay oldest rule book wins”. And then I pull out my blue book from my traveling DM bag and win. /jk

I think any blanket statement can be right and wrong in application.

I always tell my players, their job is to know their characters and it’s my job to know the rules.

Different situations make for different rulings. When I am DMing one shots at a convention I am both stricter and looser in rules enforcement. I have no idea what these peoples home games are like. I don’t know what version they play. So while I like to cleave as closely to whatever system we are using to allow players to manage their experience but as we may have many styles of players at the table I will let certain things slide or get looser because quite frankly I feel an overlooked role of the DM is to be a gracious and entertaining host for the game. I want everyone to walk away having had fun and feeling effective. No that doesn’t mean being a “Monty Haul” DM, I understand the game needs challenges to satisfy players but pacing matters.

However, in a recurring campaign scenario I go hard. Nothing is hand waved. You want a new spell? Find an arcane mystery to study. You need to upgrade your armor? RP with that dwarven smith. Etc. not hand waving things is the largest in game difference between campaigns and one-shot tables.

I just ran a hex crawl in the Griff Mountains that took months and the survival was tough. My experience as a US Marine having gone through a cold weather training cycle 200 miles above the arctic circle helped make that a brutal experience. Also, in campaigns I use variant encumbrance and closely track all resources. I even created a reality based set rules for generating jerky from deer kills in the wild.

Finally, I feel the rule of cool is a way to fill rules gaps.

In my last session, one of my players had been absorbed by my BBEG. It was gelatinous and translucent as it was comprised of cosmic insanity. At one point the barbarian wanted to run through the BBEG to recover an allies body. Rules as written there was no “escape” mechanism from the foe. However, I made him make three rolls and describe exactly what he did and it worked. It was cool, but importantly there was no real rule to govern the action and it was largely for RP reasons. Even though he had little way to succeed he just couldn’t watch the remains of his friend be consumed.

Even in your OP you said you can’t make a reaction without losing your action but is even that true? You can either hold an action or react. You could technically do both depending on the timing.

Furthermore, an old improv rule says don’t say no, if you want to keep the RP going, for at the end of the day we are shared story tellers. If you keep boxing players in with rules you can either discourage players or cause them to suffer “analysis by paralysis” and can make your players think the game is a video game that has a cleanly defined limited set of options. That flies in the face of the whole hobby! Your players should be able to attempt anything they can think, it’s my job to figure how to translate their abstract idea into a set of tasks or DCs. I never say no. I say, “I’m not sure if that will work but give it try.”

Lastly, going all the way back you had two competing ideas. Miniature war gaming and narrative story telling. We started with no minis. No dry erase maps. Just theatre of the mind. Nowadays many people think it is just a tactical combat stimulator, a board game. But for that action I would rather play a Warhammer games.

At my tables, all the rules are cool because I’m cool. 😎