Okay, but that's a disingenuous argument to be making. Yes, AP is designed with the options to block instances, but that's not the core function it's built around. That's a failsafe, not the selling feature that would make communities adopt it. Communities can already exist without federating with other platforms: by running their own, non-AP platform in the first place. The developers of AP didn't say "I want to make a protocol built around blocking connections".
Nobody buys a car for its brakes, but you still need to have them for safety purposes. Defederation is pumping said brakes. It's a necessary feature, but not the main point of the car.