Maybe the issue isn't to do with teamplay (with or without alts as everyone could do this) but more that the game is old and has very experienced players. A WCS is meant for experienced players but 10th badge gets you on. Vet servers (not had one in a while) are also meant for experienced players but the entry requirements are low.
The real question is "how do you produce a world that only the genuinely in-experienced can enter?" and as has already been stated on the forums, an entry requirement of no badge would simply lead to new alts from experienced players entering in order to win.
Frustration at the same players winning is understandable, but I don't see a solution that would work. Do you have one?