As a player I must say I'd be a bit miffed if there was a wizard standing in the back eviscerating all of the enemies. As long as I'm of SOME help I feel great with the character I'm playing. Just doing things like picking locks or going all stealth on an enemy base don't make me feel good... there's nothing quite as gratifying as doing damage to enemies.
It MIGHT be better if the wizard would be taking a while to complete the spell(say, several rounds) AND you could defend him from hazards effectively until hes done. Thats teamwork.
If instead, you were rushing to his defense when he turns into a hydra and eviscerates the opposition, much faster than you could have. Thats invalidating teamwork.
Omnicompetent characters find it hard to actually benefit from active teamwork, as they have used their resources to make them excellent at every possible task. The only benefit they'd gain is well, for tasks that require multiple actions to complete(e.g. combat), where if another character can perform that same task, the actions are additive.
However, they are good at passive teamwork, where a task requires that nobody fails(like stealth), because a failure for one is a failure for all. D&D having a schizophrenic view of role protection(you need to be good at every defense you're likely to be hit by, but you only need to be hypercompetent at one way of doing a task to deal with all tasks of that type), this does leave 'role protected' characters a bit screwed.
