The damage from the re-entry is less than what a Sage!FRS can do. Ultimate should be tougher, its just we dont know how much as there hasnt been an instance where we can compare.
Also, this is U/Cannonbolts balled up defence. Even if we were to assume that Naruto couldn't damage him (he can), what could Ben do here? Cbolt has no attacks besides rolling, and he's not fast enough to tag base Naruto.