You do realize that some people aren't comfortable with different play styles right?
I may be a god Soraka that is running around fights at 10hp, dodging multiple skill shots, and keeping the team topped off vs an absolute ass at Alistar who dies instantly every fight because I don't know how/when to engage. Sitting there and telling me I should play a champion that I know I'm bad at just means the game is that much harder for the "carries" that couldn't be bothered to pick a decent team comp and are relying on me to make up the difference from a position that is going to be under leveled and underfed for 90% of the game.
I play a ton of Brand support. Know why? Because so many of my teams lack 1) AP damage, 2) ranged waveclear, 3) CC, or 4) all of the above. Riven top, Lee Sin jungle, Zed mid, and Draven ADC. Yep, just brillant team composition right there. I had games where I'm the ADC with a Quinn top, Graves Jungle, Zed mid, and Leona support. I picked Ziggs. I will generally try to make up for whatever ass team comp my team picks, but I pick champions I'm good at, not ones I don't understand.
If I have to tank, I'll pick Blitz because I can stand in my team and bring enemies to us, which is what makes sense to me. All the champs I'm good at are poke champs. I don't play assassins or melee champs because their play style is completely counter intuitive to me.
I literally don't know how to play Leona cause I always die as her since no one understands what to do when I stun someone. As Thresh I'll hook and flay and do everything to protect and make picks but that doesn't make my team click the damned lantern when I position to save them. That 5 man flash pulverize may look awesome, but it does nothing if my fricken Yasuo top who spams "pick knock up champs" doesn't actually use his ult when I do it.
If you a decent team comp, then fix it yourself. Don't expect the other positions to make up for it because normally they won't.