wat
Halo 5 actually has a lively community. If you're talking about Halo 4, it was more of bad balance decisions that killed the game. As for SC2, League and all the mobas cames at that time which essentially killed it. SC2 didn't die because Blizzard wasn't listening to their players.
As for League, the biggest issue the competitive players have isn't Dynamic queue or autofill(Aside from a few who can't handle supporting) but the fact that the population in high MMR is actually quite small.
As for the Nintendo comment...it was a matter that they released a system that had little to no difference from the Wii aside from teh fact that it has a gamepad(Thus actually leading to confusion from the casual audience, not catering towards them), and that it was barely an upgrade from the Wii at all. It definitely wasn't them catering to the casual audience.(Although the NX does seem to be looking for that 'mobile' stint what with the rumors about it, so that is something you can say that will cater to the casual audience.)
That and over time, it's only natural that a game loses it's audience. But bad analogies don't really mean that League is losing people because Riot won't listen/caters to the lowest common denominator~
Edit~
For Halo 4, this thread outlines the huge issues that game had. And no, 'boosting' nor the ranked system wasn't a part of it