The problem with teams is the fact that unless the group can work together, it can fall apart. this is a good example IMO

Don't get me wrong, there are levelworking groups out there (OLC and XLM are two I know of) but I notice a lot of the levelmakers work solo, so grouping is not very common.

The best thing to do with your levels is get other players to play the level, and listen to their feedback. since the level you mentioned is multiplayer, this is easy: Host it!

If you let other players know that you are the author of the level and are interested in making it better, the regulars of the game won't turn down some time to critique the level.

Also, study other levels of the genre. They have little quirks that can help you design your levels.