Just on the surface, these sorts of games are notoriously difficult to balance properly. Someone discovers a strategy that tips the balance, and units/abilities/whatever have to get nerfed. The odds that there's a stable balance at a level of play not actively tested (e.g., infinite APM) are extremely low.

One example is a sibling post's video of 100 zerglings against 20 siege tanks. For humans, the zerglings are capable of destroying only a handful of tanks before being killed of. For an AI with infinite APM, they can move all but an individual targeted zergling out of the way of the tank's splash damage. This allows them to take out all of the siege tanks with only moderate losses. Many such matchups will be tossed on their heads, and it's likely that one of them is totally game-breaking.