Yeah, Paul was defenetly inferior to John in songwrtiting. I think that it still extends a bit to Rubber Soul. You Won't See Me and Im Looking Through You are ok, but they don't match up to Girl and Norwegian Wood. Sure Michelle and Drive My Car are fantastic, but thats about the only good Paul song that was good, and with pretty important help from John. After that, Paul came out with very good songs relatively equal to Johns.
I dont think Paul was having writers block actually, I think he was just progressing as a songwriter.
You also gotta remember, John was a pretty domineering guy, he was the leader of the band, and becuase of that he got lead vocal on most songs that were John and Paul 50/50s. Even though John was singing,they wrote most together.