We are going to lose the game and drop in rank and elo. Let's 4 man report whoever we liked playing with the least or whoever has lowest kda or whatever and then we don't lose anything while they do. Uhmmm... it's a nice idea, but that's why your suggestion doesn't really work.
There have been a number of games this season where I was stuck in silver trying to climb only to have mid lose, jungle ff never gank or camp for a losing lane and just feed more, and bot go 0/10/0 APIECE in laning phase alone. Before their kda reached that low, I was asking nicely for them to just play safe, miss a few cs (to live), hug tower, and not die. I would remind/ask them to please ward only to be ignored. Meanwhile I'd be going even while getting 2v1'd top for 15 min straight and holding my own. And then bot would start calling me toxic for asking them to ward or play safe. And eventually mid and jungle would side with our inting 2/15/3 bot lane who fed 3v2 over the toplaner who went 2/5/4 - 3 deaths being from teamfights tanking the enemies they fed. And somehow I'm the bad guy who gets reported while bot lane is a pair of saints who had to put up with me all game. Yeah, I think your suggestion is not the best idea. P.S. - this "get gud stay in bronze" is now gold 5. And my 0/10/0 teammates from those games? You tell me where they are.
I'm not saying I'm amazing or they are trash. I am saying we should never have been at the same rank or in the same game. And because matchmaking puts such variety of people together, your reporting system would easily be abused and not achieve its intended purpose.