I personally think teaming is just not cool. Sure, it can be really fun for you and your friends, but think about everyone else in the game whos experience is being ruined because you and your friends decide to team up? I've been a victim of this SO many times, I've gotten used to it, but lots of other people get really annoyed by it. Anyways my point is, I understand the appeal to it, and how it can be fun, but overall it ruins more fun for other people than you get out of teaming.... if that makes sense... I don't really think there's a combination of words in the english language for the point I'm trying to make... anyways you get the idea
And for the point that it helps people improve, literally doing any kind of pvp helps you improve. Just hop on a duels server and do some 1v1s, nobody has the unfair advantage, and in my opinion, is the best way to develop your skills.