The future, is in the past... ONWARD, AOSHIMA!
I think one of the best ways to nerf Drake's barrel is to nerf the air version, as Drake players get way more mileage from it. You mostly see Drake players hop up before using the barrel. This is because Drake drops as soon as he launches the barrel and can perform an action as soon as he lands, making it appear as if he has almost instantaneous recovery from it. I say it's best to keep Drake in the air for a short time after he kicks the barrel, maybe not as long as he takes to recover from the move on the ground, but enough to ensure that the player can't immediately follow up on it.
I could probably suggest the same for the golden gun shots for his level three. There's a reason the ground version has so much darn recovery.