This is definitely not true of bucket hashes,

Yes. It's not true. Those examples use pathetically tiny hashes (which were reasonably sized back in the 80s when Pick was big). These days, with the memory hierarchy being what it is, data sizes being what they are, and rehashing requiring massive pointer copying at best... well, just you try to rehash a hash containing fifty million elements and tell me that it'll not be slow enough to notice. (And this is not particularly large as such things go.)