If RuneScape does go on Steam, they will surely get enough new players to make enough cash that the 30% would be a non-factor. Can't speak for Epic though even though it's just 12%, they might not be able to recuperate the price should they go on there. It might be moot. Game stores give large access but don't have player retention that is needed for an MMO.
It might be rapid short-term profit, but any new person wouldn't be expecting this kind of game to be in the shop leading to just F2P or only 1/2 month subscription. Then you would need to deal with the negative reviews which are likely to come out of them because RS is a really slow build up to end-game content compared to the normal action-packed or speedy gratification of the other matches on the stage. Why would being on steam give enough money? We are not only discussing the cut, we're talking about the money spent making RuneScape meet the requirements steam has.
I don't know what they are but they're at least going to include composing a launcher that can work through steam. Steam distributes updates for games on the stage so again you need to get a means to get the update. Not impossible tasks although not 5 ones. And you have to ask, what could it perform? Runescape's problem is not that people haven't heard of RuneScape - it is that people do not wish to play it. Even people who have never played an MMORPG in their life have heard of runescape.
The problem is getting them to play, would that be helped by being on matters like steam? Perhaps, but it's not certain. I might be speaking out of my ass here, however, steam has games using their launchers. The RuneScape client has its own launcher without a user interface. They would just need to get the wrapper on steam/epic, which would just need to get upgraded when there are major client updates where you need to redownload it from the website (which does not happen often, right?). Not sure how they'd handle revenue sharing. All RuneScape purchases are done through a weblink rather than in RuneScape game, but they could mplement a steam shop for runecoins / keys.
Yep plenty of steam games have their launchers but from what I have seen they manage updates via steam rather than via the launcher. Meaning every week they would be pushing updates through steam as well as through Apple, android and the present desktop client. Yeah that on its own isn't a deal breaker but all these little things accumulate very fast to make a simple suggestion"put game on steam" into a pretty major project with plenty of possible drawbacks.
Ohh and valve would like you to include steam wallet as an option even in web link shops. And any in RuneScape game purchases have to be locked so that a player accessing via steam can pay via steam. Basically, they want their cash, you can't blame them but it is full of negatives from the perspective of jagex. You also have the update process generally, I do not understand what kind of lead time steam need with upgrades being pushed and if this will work with how frequently RS is upgraded. Many, many mmos possess their own launcher, and steam updates only upgrade the launcher. FF14 comes to mind as a example. The launcher is kept by steam up to date, the launcher stains RuneScape, entirely outside of steam.
The details of the game information in https://www.winrsgold.com/