Cutting & bulking is not fitness, it's muscle building for appearance and status.
A good level of fitness can be achieved and maintained with an hour of separate core and aerobic exercise per day. You might not look like the guys in Men's Health but you'll probably swim a hell of a lot better than them.
There's more than one kind of fitness. Bulking and cutting optimizes for maximum power-to-weight ratio. I won't deny that there's an element of vanity to it, as there is with any effort to be fit, but that doesn't make it "not fitness".
To borrow your phrasing, someone who follows GP's program instead of yours might not swim as well as you, but they're probably a hell of a lot stronger.
A good level of fitness can be achieved and maintained with an hour of separate core and aerobic exercise per day. You might not look like the guys in Men's Health but you'll probably swim a hell of a lot better than them.