I dont really agree with this. KOF's most popular iterations are ones like 98, 2002 and for whatever reason 97 in China. Those games arent THAT complex in comparison to XIII which didnt really do that well despite a great artstyle. XIII had an insane execution barrier, XIV is easier but still not an easy execution game and I think its unfair to call it 'simple.' Either way KOF is and has been doing fine. Its only USA that doesnt get hype about it.
With Marvel I agree and I disagree. I agree because part of the reason MVC2 lasted so long was because of its complexity (Probably helped that Marvel 3 didnt happen for another decade). But the mechanics themselves were not complex and the inputs were easy compared to other fighters. Pushblock, snap, DHC and team supers. All easy inputs and easy to understand. You can fill the screen with a team super just by pressing 2 buttons together. Marvel proved that easy inputs =/= easy game. Plus just look at those mechanics, all of them useful and fun to use. See thats a big difference with accessibility in 2017 and accessibility in 2000. DHC in marvel 2 is easy and fun. V trigger in 5 is not fun. Crush counter the same. Most of the big complaints of SFV arent really complexity but problems with the mechanics and the core gameplay instead. No footsies and stub normals for the majority of the cast. Forced easy links/combos (casuals probably still dont know what a 'link' is even though they made it easy). I guess the point here is MVC2 did have accessibility for new players through its input leniency and easy inputs, and yet maintained an extreme level of depth. Capcom in 2017 seems to struggle to do that, instead alienating both the casuals and the hardcore players.
What I personally didnt like in MVC3 (and this is just my opinion!!)was actually too many mechanics. Take MVC2 and add TAC, X factor, and artificially lengthen combos with the ground pick up. All the mechanics added were abused ad nauseum, which to me is different from MVC2 where the broken ness mostly just came from the games core gameplay. And the really real point is MVC2 thrived not just because its complex but because that was the perfect storm. All the goodTV cartoons from Marvel, and Capcom came through on fire with gameplay, came with a great artstyle and included EVERY1 you ever wanted. This should never be forgotten
I think moreso than complexity, FUN and the visuals is what keeps the games really going. If it was all about complexity then Blaz Blue version 5000 would be the most talked about fighter on here.