I find the biggest thing people get wrong about this game is the matchmaking. Going to go on a little rant because it's crazy how many people don't understand the system.
People will watch high level players stream and complain about the system (while most still don't understand it either, some still have the misconception you can win <50% of your games and be rank 1).
No, the matchmaking is not terrible for you and no you are not constantly going into 5 stacks. The reason high level players complain about the matchmaking is the 6 minute rule. After 6 minutes it will just pair you with players so you can play, not really caring about group size or MMR difference.
THAT IS NOT HAPPENING TO YOU EVERY GAME. Your team is not beneath you and you are not some pro that deserves rank 1 but your team is holding you back.
I went from 50 to rank 1 about 90% solo queue at various times and for as much crap sites like hotslogs gets, there was maybe a handful of games where our hotslogs MMR was more than 1-200 apart and that still isn't drastic.
Now onto the group aspect, do not go into games with 2+ people then go "OMG why are we against this 5 stack". The game will prioritize groups be paired with groups. While it sounds stupid, you should realize that the game is majority based on team work and coordination. Also on the point of grouping, if you go in duo it will try and match you against another 2-3 man group. If you go into matchmaking with 4+ it will match you against 4-5 player groups so even if you are a bit lower on MMR, don't be surprised to run into better players here as in my experience there isn't a ton of lower MMR 5 man stacks queuing.
And lastly, stop taking losses so harsh and getting on tilt. Some games the matchmaking is setting you up to lose. By pulling through and winning with seemingly terrible teams, you are bumping your MMR up a lot more than when you 10 minute rofl stomp a low skilled team. The last team you just had that just couldn't figure out how to plug in their keyboard and play correctly will most likely not be on your team ever again, at least not more than a few games.
TLDR: Matchmaking isn't as bad as you want to believe because you are losing games. Do not take your anger from previous games into your next one.
Kind of an incoherent rant, on phone and just woke up.