From what I read, he was the one that pushed for the first four being released in mono.
There's been so much revisionist history with these guys you have to wade through so much to figure out what's what. Lately, GM has said that he had nothing to do with the stereo albums until around Revolver, and that Junior engineers did them back in the day. George Harrison claims he didn't even know you could buy those early albums in stereo back then.
It has been confirmed that they put all of their work and time into the mono mixes, and that the stereo mixes were done really quickly, shortly before they were released. The audio evidence bears this out.
That changes with the White Album though. They put more work into the stereo version, and that's obvious when you hear the mono one (which is disappointing IMHO).