Many of the early Beatles stereo mixes have what we would now deem "strange" panning. But you have to look at it in terms of the '60s
Stereo was new and a novelty. It was a special effect. Most people still had mono equipment any way. It was seen more in terms of "Hey, we can get the sound to come out of two separate speakers.." rather than thinking of them as a stereo image pair.
So if you imagine a typical '60s home with a new stereo system, the speakers placed randomly in the room because that's the only place they will go... Drums and guitars coming from one corner by the door while Paul sings on his own over in the other corner by the window...
It must have been magical.
Quadraphonic was a logical step from stereo. Spread the speakers around the room and you can have a different instrument in each speaker, just like having the band in your own front room.
They were thinking in terms of the number of channels they could separate the sound into rather than how many speakers it would take to create a particular sound field, which is what we do today with surround.