at the same problem with 4 teams control point and capture the flag:
1. the team aren't so big 1-4 players per team
2. no all the teams will be filled
3. I almost guarantee that small groups won't defend their bases or prevent someone to push
For 4 team game modes, the game mode has to be like capture and hold (Like KOTH).
I tried this with CTF, CP_hydro tried, and payload won't work. the teams gets stuck and the gameplay is almost frustared.