This was definitely a time when Lewisohn blew it. When his book came out, I even wrote a letter to him, via his publisher, asking him how he could NOT hear the organ on the track. Never heard back from him. Granted, it does blend in with the guitar riff so well that it might be hidden to some ears. But when separating the stereo, it is much more audible. Nothing that Ringo couldn't handle.
Prior to Rubber Soul, Paul did very little guitar work that has been documented: "Yesterday", "Ticket To Ride", and "Another Girl". Am I missing anything? On Rubber Soul, much of the album has an unplugged feeling to it. I suspect that Paul had been champing at the bit for a long time to do more guitar playing, and for whatever reason he played lead twice on the songs from Help, he did prove himself to be a competent guitarist. On Rubber Soul, there could have been plenty of opportunities for him to strap on an acoustic guitar and go at it.
To me, the acoustic guitar on ILTY does sound like Paul's style, not John's. On other tracks where John played tambourine, I always thought his playing was, um, unique to say the least, and it sounds like him on this track. I have to agree that the lead guitar bits on the middle eight sound like Paul. As for the riffs between verses, George could play them, but it does sound so un-George, you may be right.
Drums? I think Ringo, in spite of the missing rim shot. Maybe that rim shot eloped with John's missing chord from "She's A Woman".
What else did they record at that session? Was George there for any other tracks that day?
Personal observation: We'll probably never know the truth, but I've long suspected that Paul became dissatisfied with both George's and Ringo's playing long before the White Album/Get Back sessions. One of the things that made G&R valuable to J&P, in my opinion, was that they were content to be role players in the early years. J&P could arrange their songs and direct Ringo (for sure) and George (to a lesser extent). No doubt they could never get Pete Best to play what they wanted (mostly do to his lack of range on the drums - a real reason to dump him). And can you imagine Paul trying to dominate Clapton had he replaced George? I think not.
Even John used to complain about Paul wanting to experiment with some of his (John's) songs.
Don't misunderstand, I'm not bashing Paul. Just saying.