I think that :
In the lobby, the players should be able to define their team but not to start as infected or survivors.
At the beginning of the game, the server will complete teams (as currently) but then, the server will randomly selects a team to start as infected.
The team that started as infected will start as survivors in the next map.
I think that simple idea could help the balance. That will avoid that good players teams create a lobby and choose to play first as infected first.
Hope for replies,
dV
ps: i'm french so i also hope that this post in english is understandable.