Why is matchmaking in normals so incredibly bad?

It is amazing how in every single game, every - single - game, the teams are so unbalanced that they all end in stomps. In the last few months I have not had 1 game where everyone was around the same elo. Golds playing vs masters, a 5 silver premade vs 4 plats and 1 diamond, a low plat vs a challenger, I've seen it all already. Today I was playing Lee for the 2nd time ever in teambuilder, and apparently I had the right to "matchmaking adjustment" (= play vs less experienced players because you're new to the champion). Guess what, there's the #200 best Rengar world in my game LOL. The other day I queue up as Ahri with some friends and I have to lane vs a 700 LP Challenger. I can't premade with my gold or lower friends at all because matchmaking is so unforgiving that they'll be playing vs a full diamond team. Yet, when 3 master tiers premade, they get to play vs some low plats. It got to a point where I have absolutely no fun and no reason to play normals on my main account because it's literally just luck. Either I get the master/diamond teammates tryharding on their main champions and stomp, or the golds/plats first timing something who get completely stomped and thus I lose. But what upsets me the most about all of this is how simple the fix would be. Here's my suggestion: if your ranked mmr is higher than your normal mmr, your ranked mmr is used in normal queues. This way you don't get the brilliant matchmaking everyone complains about on the boards every day. And people can actually enjoy the game when playing champions they don't main. It is just such a hostile environment when trying to learn a new strategy, role or champion because the system assumes you're always playing at your best, and with your best champion, even in teambuilder. "Matchmaking adjustment", lel.

TL;DR: In normal queues: If ranked mmr < normal mmr, normal mmr is used. If ranked mmr > normal mmr, ranked mmr is used.