Not really. It would obviously only be half as good as each individual ship(a BB or CV), but it would also be much more versatile, and in alot of situations that's what matters most.
The planes could act, depending on the situation, as (extra) fighters to fend off enemy torpedo and bombers, or sent out to aid in bombardment of a target. The guns would then also serve a dual purpose. They could be defensive, protecting the BB/CV proper, the fleet as a whole, or as gun support. They'd serve as a good all-around platform to make up for whatever may be lacking one area or another, without having to divert a dedicated BB or CV.
Think of it as a sort of insurance policy. Might never need it, but when you do, even if it isn't the best, you're elated to have it.