This could be because when people think of someone sneaking around, they think of them being alone, which implies, even with modern comms tech, that they aren't working with others.
It's also because being a high risk, high reward role, you spend more time dying/hiding and less helping.
However, just because you spend less time helping, doesn't mean you're less helpful, because wheny you are helping, you're helping loads.
That's because people are fools, hung up on the idea of teamwork requiring communication or being near each other, neither of which are explicitly true. A lot of it really boils down to the predjudice against "snipers" in most games leaking into Brink. People think that being away from the team means not playing as part of the team, in part because people are stupid (as you can see, I've suffered the negatives of the belief and am thus bitter at said people).
It's the same thought process that occurs when people think that players that are out for kills are useless in a game like this. Somehow they forget that part of being a team is being a collection of different players with different skills and purpose working toward the same goal. It doesn't mean doing the same thing, or doing things the same way.
Medics need to be near the team to be effective. Soldiers need to be near the enemy to be effective. Engineers need to have a goal (usually defensive) to be effective. Operatives need to have a goal (usually offensive) to be effective.
The team work begins to sort itself out because the soldiers move toward the main enemy and the medics follow. The engineers move to secure objectives, or the area in which their soldiers are fighting, and the operatives either drop into a defensive position or bolt to the other side as quickly as possible in order to get past the initial enemy rush. Where the natural progression fails is that sometimes you have 6 operatives and 2 soldiers so the battle gets brushed back too quickly, or you get 6 soldiers and two medics, so you get slowed down my lack of information, or being flanked because you have no defense playing.