Think they hit stronger?? I really do not know, but consider you canwin a trophy with petpet battledome http://www.neopets.com/gamescores.phtml?game_id=231
Actually, they do fight, and that's the main way to level them up (besides the petpet lab ray). That said, doing so is utterly pointless unless you enjoy that sort of thing.
Once upon a time they were usable in the battledome. I'm assuming level played a part in that, but that feature has been disabled.