A lot of moves are the same when it comes to most defenses, I think the counter gambits deserves some extra study but most defenses is Nf3, bc4, O-O, play d4 or d3 to safely regain the pawn or battle more strongly for the centre etc.
But off course the higher you get, the more you wil have to learn. The thing I like about the king's gambit that development feels very natural. If you play it a while you will learn a few schemes to play as white which can be used in almost all the variations.
Given that, you have to learn to play against a ton of different defenses (to name some):
And all your opponent has to do is pick and learn one of those. You are spending like 10 times the amount of time as your opponent. I suppose the benefits are that it is fun to play and can serve as a surprise weapon against some players.