Not really sure about this tho, but i think it wasn't possible in ETPub to join a team when it only has 2 bots vs a team that has 5 bots for example?
On the other hand, yesterday i joined the server and it was 5v2 without bots. I joined the 2 that made it 5v3, just one message in chat to ask if anyone would be so kind to even up the teams did the job and we played 4v4.
Key in balancing team is to communicate with eachoter, and also, unfortunatly, sometimes you need to give up a good gameplay to switch teams.