First off, how can you claim RCS "requires you to buy an Android and then state iMessage is "cross platform through Apple's ecosystem? RCS works on Android and is available in various devices from many manufacturers. iMessage is only available on devices sold by Apple.
Secondly, why would you rate iMessage higher than RCS for "ease of use"? That makes zero sense, they behave basically the exact same way.
Lastly, RCS is coming to iOS - Apple's just been lagging because implementing a cross-platform solution is detrimental to their profits.
So RCS will eventually work across iOS and Android AND work by default. There's no reason RCS wouldn't be easier or rated higher than iMessage in terms of "ease of use"
You're right, I forgot how Matrix handled messages and the current state is that there's are at least 6 other clients that support E2EE - this is awesome.
That said, as soon as you look for a stable client that supports other features like Native 1:1 calls and Threads the only client listed is Element, check here: https://matrix.org/ecosystem/clients/
Side note: Looks like ~3 years ago a Fluffychat dev stated they would not implement E2EE in the app [0], this must have been around the time I was looking at other clients because I recall this one "looking" the best and might be viable for non-techy people to use/recommend. I'm glad they changed their mind and implemented E2EE. Time to take a look at it again.
[0] https://gitlab.com/KrilleFear/fluffychat/-/issues/25#note_423061121