The smaller teams are, the better it is in public play.
8v8 is already quite a mess, imo. If the automatic communication system in BRINK works as described, however, it could work fine.
Depends on your perspective.
In Assassin's Creed: Brotherhood, you have 4 vs. 4 team modes, and 3-team 2 vs. 2 vs. 2 - In either of those, the small number of players makes it relatively easy to coordinate, but a single idiot or griefer on your team becomes a CRITICAL liability.
In Brink's 8 vs. 8, the team coordination becomes more complex, but at the same time, one problem teammate will have less of an impact on the team's effectiveness than they do with smaller teams.
There's a balance to this, and I think Brink has struck it just right for the way they're making it - objectives would be MUCH too complex with more than 8 players per side, but less and you're risking too much on a single bad egg.