You’re mistaken about the PDP-10. Yes, you could pack two pointer-to-word pointers into a single word; but a single word could also contain a single pointer-to-byte. See http://pdp10.nocrew.org/docs/instruction-set/Byte.html for all the instructions that deal with bytes, including auto-increment! And bytes could be any size you want, per pointer, from 1 to 36 bits.

Not to say that I disagree with your main point.