Probably a wise idea.
One thing that differs BRINK from Team Fortress 2 is that having "too many" of same class can actually work. For example, if there are too many soldiers, they can fill many roles (some are light body, some are heavy, everyone might prefer different weapons and playstyle variations). They are not stuck with using the same basic strategy like a team of 8 scouts in TF2 would be.
In fact, you're quite mistaken. Whilst Scouts work sometimes, a team only composing, say, Soldiers will destroy absolutely every opposing team that is not specifically constructed to counter that, and I've played
multiple games where a team entirely composed of Medics (yes, TF2 Medics) can win a game, even on attack vs. Engineers, Snipers, Demomen, Heavies, the lot.
Class rushes with anything except Sniper and Spy are very, very effective.