For cheaper keycaps that come with an office or "gaming" keyboard, sure, but not for higher end ones. PBT doesn't shine after a lot of usage like ABS, true, but high end ABS keycap colors and the sharpness of double-shot legends still tend to be better than PBT (e.g., GMK). Sound and texture is quite variable too, so it's really just a matter of preference. I've used nice PBT keycaps but tend to prefer how nice ABS feels and sounds better.

I’m not too surprised because PBT as a material is harder to work with. It’s more prone to shrinkage and large caps like the spacebar are prone to warping, and this compounds if you try to do doubleshot PBT.

Most of the affordable PBT caps I’ve seen have been dyesub (which can be very durable if done well) or PBT-ABS blend doubleshot.

Absolutely.

By any objective measure PBT is the winner in all regards.