Drain = power level 0 in a scala from 0-6?
More like power level 10 in a scala from 0-6!
His skill would obviously be very useful in suppressing other power users.
He would simply need to get close to them and they would be drained.
At the same time even normal people could take him out with some normal ranged weapon.
So his skill is the ultimate skill to keep other power users under control or from going berserk and in capturing criminal power users while he himself could easily be stopped by normal policemen, government agents or so.
Heck! The premise that draining others is not useful is obviously only done by the author just so he can create a story around how that "bad" power turns out to be extremely useful and powerful.
Otherwise he would actually have to come up with a real storyline about the obviously OP MC.
Someone already said it but his power is actually pretty useful. I mean, he would have to be kept close but he could disable dangerous power users. Heck, he could be a bouncer or bodyguard. It's actually not all that bad a skill except for the range.
It's described as drain, but no explanation really on how powerful the drain is.
If anything, I would suggest him to be a police negotiator.
*Goes into the building to negotiate*
*Makes all the bad guys unconscious*
*Calls in the other guys*
Additionally, as a prison guard / prisoner escort would work.