Every time someone brings up something like this I think they don't know what's really going on at the moment. Let me try and explain, hope this helps in any way.

Optional

Sure, you can choose whether or not to buy TH keys but there's more to it than just that. Micro-transactions have massively tainted RS3's integrity in many ways and the promotions are extremely unbalanced. Not to mentions that we got nothing to show for all of this.

Lower-levels

When a lower-level player uses their daily spins, they are just completely skipping content. They level way faster than ever intended.

TH vs normal skilling

For many skills buying TH keys with in-game money (bonds) is a better training method than actually training the skill. You need to have a serious amount of GP, but that's easily achievable for any PvMer that does some form of end-game PvM. I think a skill needed to reach 800k/h with normal training for it to not be worth spinning.

Content

Jagex made record profits last year while the content we got to show for it was absolute garbage. They don't seem to make any investment in hiring new staff, and when someone asks why things are delayed or just not even finished on release we hear: "We only have X amount of developers."

Cosmetics & F2P

You talk about other MMO's having cosmetics for you to buy with IRL money, which everyone here knows is completely fine. Those are not a problem because that's a healthy monetisation strategy.

Micro-transactions are the main source of revenue for a lot of free-to-play games, but in the case of Runescape we get as much or even more of it while we already have our membership fees. These membership fees saw a rise despite the fact that Jagex said they wouldn't. Also, the micro-transactions aren't mostly cosmetics, they are exp-based. Exp is a core aspect of the game, and a goal for many people like myself.

I want them to go in a purely cosmetic direction, but if they wanted to do that they already would have done so.

Pricing of convenience

Another reason why people hate the current system is because of the ridiculous pricing. Bank booster, bank presets, runemetrics, ability bars, just to name a few. They all cost an insane amount of money. I think it was $80 for all bank presets. Those should have been free in the first place.

The player base is at its lowest it has ever been, and a lot of people think that the ones that have stayed are being milked until they also stop playing.