How do you play this game for 7 years and make a suggestion like this?
All of the "problems" you talked about in your post have the same solution: get good.
A two person deathmatch isn't a deathmatch, it's a duel, and if you want to play duels you can go to a million other Minecraft servers for it.
A four person deathmatch would be fine, but not if it's split into 1v1s, because again, that isn't a deathmatch.
If you are allowed to team with any amount of people during the actual game, why would you think there shouldn't be teams in deathmatch? The option is available to everyone who plays, either play better and kill the teams yourself, or find a friend to play with as a team. Or just lose and don't complain.