Diamond 2 is so frustrating

I grinded for three days from Bronze all the way to Diamond 2 and every time. EVERY STUPID TIME I'm one match from Diamond 1 I get. The. Most. Stupidest. Players. Ever.

Then I get sent down to the negative amount of Diamond 2 and I just got demoted to Diamond 3. What is going on here!? It's not like "oh I just had few bad matches" NO. I been grinding for three days and always. ALWAYS stuck in Diamond 2. Then the audacity I had with a played who literally bans Loki "because I don't like him". It absolutely sabotage the game because he knew I wanted to be Loki and he disconnects during the match leaving us with an absolute lost and guarantee win for the enemy.

I love competitive it's so nice to be around competent players who knows what they're doing. But diamond 2 feels like just either filled with the most idiotic players or the matchmaking is absolutely rigged. I never had 8 losing matches in a row during my climb.

Edit: examples of what I've been put through.

Moon Knights who are in the negative scoring and keeping playing.

Enemy teams who SWEAT. Like Jeff is some how getting up and close to Iron Man and killing him out of the sky sweat.

Spider-Men and Venoms who only get 4 deaths and zero kills.

Tanks who don't tank

DPS who get zero kills for the first five minutes of a match

A Hulk who is way too focused on throwing Wolverine

Getting dived by Starlord, Hulk, Venom, Scarlet, Magika, MK and the team DOES NOT CARE

I once saw a punisher shooting in the opposite direction, ignoring the enemies coming out of a portal behind him

These are like Bronze minded players. Why are so many diamond players act so stupid so make unbelievable players that hurt the team!