Lol, not true. In EE for example because you didn't watch your casualties, you just assaulted blindly, which, while having beaten the bots, caused you a lot of losses. That would have been devastating in a pvp. Most of the games that actually allow huge armies have a big resource handicapped, their accusation is were close to war3 speed, which means that you need a lot of time to make them, or you start at a death mach mode, where you got loads of resources that you can use to make a huge army quickly, and then use incoming resources to replenish losses, problem is if you lose more then you get resources, or more then the enemy your in trouble. And that's where real strategy comes in to play, since flanking, or bringing in 2 surprise bombers over his stacked infantry really counts.
Units usually have very bad path finding, so its way better to split your army in to squads and assign em specific targets then you group em all up and send em while they block each other.