In skywars skybasing is against the rules so you're it's not against the rules cliché is a bit all over the place as it is pretty much going through
99% sure that that's completely allowed.
From what I've experienced, it's only against the rules if they are in a nearly unkillable position, forcing a stalemate.
Examples: Bridging to the corner of the map to make a big fortress there, Diving underneath the island on maps like UnderDaSea & camping there in a fort, Going to the sky limit & shoot/bomb everyone who tries to come up, etc.
Camping = When a player decides to stall & shoot everyone that tries to come towards them. Not completely unfair, as you are still able to bridge slowly but surely. It won't cost you the game because of them having an unfair advantage.
Skybasing in my opinion is still somewhat fair, but it's currently against the rules & therefore not a viable strategy.
Hacking & teaming gives you an unfair advantage, so of course you can't get away with calling it a "Strategy"