My take on this situation is that even if the classes were balanced so that you could run 6 cav and be countered by 6 inf or some combination. I feel like those games would be alot less fun to play. I feel like 3-1-2 or 4-0-2 are the most fun compositions with the current amount of players, because there is a healthy inf fight (if 2h were nerfed) and still some heavy impact from the non inf classes. If the game became a 1-0-5 or a 2-0-4 or even a 0-3-3 I would be less interested not just from a balance perspective but also from what I enjoy from the game.
Edit: I would also hate a 6-0-0 composition, because those matches would be way to static