I think that would actually ruin his whole arc. He's strong because he can learn from and rely on his friends
Fair opinion, but the way I see it, he'd only get his hypothetical unique skill back
after the arc's over. (Re)Gaining his unique skill afterwards wouldn't negate the fact that he succeeded in saving his mother without it.
He'd just get a new power for later (and he'd still have to learn how to use it).
Now, if he suddenly developed a unique skill in the middle of battle,
that I'd agree would ruin it.
Unless it was something that just let him control items better or let him coordinate with his friends better. A skill that just made him a bit better at what he's already doing would be fairly decent.