No, it just means it will always survive one attack due to Sturdy. After that, it'll have 1 health, and be knocked out by almost anything.
The idea of the Aron is question, is to use it in a SS team (or any other residual damage, but SS is preferred), where it uses Sturdy to stay alive at 1 health, and then Endeavour on the same turn (being level 1, it'll move second) to bring you down to 1 health, after which SS damage will kill you.
But you can easily beat it simply by using Taunt, to shut down Endeavour. Or, entry hazards to stop it's Sturdy from ever activating. It's certainly not unbeatable.
EDIT: quasi-Accelgor'd
Anyways, it's a real gimmicky pokemon, so it's likely you won't even see it that often. It's like FEAR, hilarious but not very practical.