The only single issue that has always held mythic plus back and not let it have the light or shine is due to only one single factor.
Players think they are better than the other player and they think if they are doing little higher dps. In the head they feel they are carrying.
The only way to fix mythic plus and its players is by improving the report system. Our reports should be looked into. If an X player is going out of his way to create disruption and cause us to loose. Then he needs to be checked.
The other suggestion is bring an avoid system in keys. Give us the option to avoid 10 players for the season.
What is the reason to even play with the player who is going out of their way to throw just cause we initiate a /abandon.