I don’t know if it is possible to have “pay to skip” not become “pay to win” in an MMO.
The whole point of an MMO is that your character progresses and gets better as they do more things in the game. If you are paying to skip something that makes your character better, your character will be better than if you didn’t pay to skip that.
If what you are skipping is not making your character better, you wouldn’t be doing it in the first place.
MMOs are be definition pay to win. You either pay with time or pay with money.
People getting around games ToS' will always be a thing - since Runescape is the example being used, it is expressly banned to both purchase and sell gold coins. This is not a problem exclusive to MMOs, it's a problem with any game with a leveling system, currency, or items that are tradable between players.
Examples: FIFA packs, Runescape/MMO gold, League of Legends accounts/boosts (names as well) , Valorant accounts/boosts, CS:GO items (names, accounts and boosts as well), Neopets items and gift boxes, Diablo 3 boosts/accounts, and on and on...
Then maybe it's fine to be "pay to win"? Seems like millions of people are enjoying their time spent, and are willing to spend more time to continue to win.
The presence of aggregate societal harm tends to be the motivator for other regulation around otherwise voluntary behavior such as gambling. So if that harm can be demonstrated then there may be a case for legislating if companies can offer such games and on what terms they can do so.
The whole point of an MMO is that your character progresses and gets better as they do more things in the game. If you are paying to skip something that makes your character better, your character will be better than if you didn’t pay to skip that.
If what you are skipping is not making your character better, you wouldn’t be doing it in the first place.
MMOs are be definition pay to win. You either pay with time or pay with money.