I think it's a valid comparison.
How is it a "valid" comparison by any rational standard? Fragmentation implies incompatibilities between devices, and in the case of Android, two versions of the exact same handset may have completely different setups and compatibility due to carrier control over OS updates. USB-C doesn't make the 12" MBP incompatible with any existing Mac accessories, you just would need an adapter to connect them. That's not fragmentation at all.