Speaking as a player of a character who is a generalist covert ops kind of person, my character does very well. He can not only sneak around, but bypass security, tail a mark, disguise himself, impersonate another male human, run, swim, flip, and climb, and does well in fire fights and close combat. In fact, I picked up some extra stuff from the martial arts PQ's in Arsenal so that he could get himself out of trouble when he needed to.
He has about two dozen different skills to cover a variety of situations. He isn't great at any one thing, he's just good at everything. Has dice pools in the 8 to 10 range for everything he does. I can personally attest to the fact that you don't need 12+ dice pools to be effective. You DO have to know what it is you want to do, and how to squeeze every advantage from a situation. I don't mean just extra dice, I mean thinking on your feet and changing the conditions that you find yourself performing in. That means making hard rolls (high thresholds) into easier rolls by taking the right piece of gear (field kits for stuff like electronics) or by making it so that you don't need large dice pools to be effective. Don't hit something head on, go around it. This holds true for everyone, but the generalist will shine if you adhere to this idea closely.
The great benefit of the generalist is that if you have someone in the group filling a role and specializing in it (becoming a primary with 15+ dice in a relevant pool), that teammate knows that, no matter what, someone can back them up when they need it. And the whole team knows that they can count on having a secondary to allow the team to multi-task a situation to their maximum advantage.
Having more than one primary filling a role is problematic as the ones involved will step on each other's toes. The generalist, however, won't outshine the specialist at what he does, but will give the team a safety net for their plans if (when) things go wrong.