How important was individual skill in formation fighting?

[Pompeius Major]

Isn't the boring answer that you need both? Individual training builds confidence and weapons handling which helps cohesion, thus ideally helping team tactics. Troops that are not individually well trained and confident in their weapons and abilities would appear to be more shaky.

I think it's more a matter of there being cases of indivudally skilled warriors that for various reasons (such as lack of group practice, uniformity, or command and control) would not perform up to par in group combat. Examples of this could be everyting from gaudy aristocrats to tribal warriors.