Why does champion select revolve around auto fill and not elo?

We went from a system of who is the highest elo to who isn't auto filled. By having players choose two roles and on the risk of being auto filled it discourages on one tricks that aren't support, and increases the chance of getting a poorly composed team. You ever check your teammates match history before the game starts? You get your main role, however the other 3 players on your team main ADC(example), thus they aren't skilled or capable in other roles or even their secondary. The enemy team however does not have that problem, with the elimination of solo carrying several seasons back, you now have an extremely high chance of losing the game. The system doesn't take into account who's role is what when they are trying to form teams as quickly as possible. Now I'm not saying this happens frequently, but it happens in smaller instances when it shouldn't occur at all.

Now another problem, by sacrificing quality of matchmaking for speed of being matchmaker, let's say you get your main role, most of the teams are picked and then someone dodges. You get a queue pop up almost immediately, voila you just got auto filled and most likely so did somebody else. Now you're stuck hoping the enemy team has just as many auto fills as you do.

And let's talk about support. Support is a role that should NOT be auto filled at all. Almost everyone who doesn't support HATES IT. This has been apparent for all stages of this game. Support is one of the most important roles in this game, if you have an auto filled support, chances are they are angry or not good or even don't care and want the game to be over some way or another to get their main role the next game.

In an MMO there is a reason you wait a long time in queue as dps, you want good tanks good healers. If this game is reliant on a good support and you don't have to wait for a good one, what does that say about your team or the enemy team? If they didn't get auto filled (I have queued support and gotten top while someone got auto filled into support before), they have a higher chance of winning.

Instead of focusing on speed why not focus on quality? Games already last 25-40 minutes on average, so why have a higher chance of losing for that time than have a balance.

And as for the hidden elo system, even if someone is on a loss streak let's say in diamond or platinum, why let them be matched up against silver/gold but still be in their rank? Instead it should stop at one tier below their rank and demote if they can no longer win games. To add, instead of demotinging players faster front division to division, demote them faster from tier to tier. You only have one tier to cross, but you have five divisions.

Quality quality quality.