Exactly. I remember being stumped when I read that Who's Next was the first record to feature synths 'seriously', and then remembering that Abbey Road has a number of Moog synth parts (recorded 1969).

Indeed, Pete made the source sound by feeding his Lowrey home spinet organ through an EMS VCS-3 synth module, which is amazing and all, but technically isn't real 'use' of a synth (to whereas the parts on Abbey Road are).