I disagree... to me it's like playing football and only using 5 square meters of the field. Sure, you can focus on dribbling action, but there's much more scope in the game than that
Larger maps to me are effectively the linked smaller maps that many people want to see. No more need for entry VLs. You can always play with the size and location of the deployment zones (the Combat Mission series uses a similar system). But at least you have a continuous and logically connected battlefield.
That means of course that you should also be able to play with more than 15 teams. Personally, I don't see much difference in handling 15, 25 or whatever number of teams. I play exclusively H2H, and I really don't see people perform better if they have 5 units instead of 15. Even now, with 15 teams, you focus on one piece of the battle at a time...
The current team order system (defend, ambush, etc) is already well suited to handle more teams. Athough you might make a case for introducing definable arcs of Infantry/AT defense, in order to introduce more flexibility in the standing orders; again see Combat mission (no I don't own stock of Battlefront , but I think that CM introduced some very good ideas that can be applied to CC as well).
And if the AI is not capable of performing on a bigger map, well, then IMO the issue is with the AI, not with the map size. But to me, getting a competitive AI is something like the Holy Grail of gaming: many tried to find it, nobody has really succeeded (that is, without cheating or sacrificing realism).