In one of his last interviews John actually made that point with a bit of bitterness and seemingly critical of Paul for not being willing to take risks with his own songs.
I guess you're talking about this John's quote in his Playboy interview from 1980:
"The Beatles didn't make a good record of 'Across the Universe.' I think subconsciously we... I thought Paul subconsciously tried to destroy my great songs. We would play experimental games with my great pieces, like 'Strawberry Fields,' which I always felt was badly recorded. It worked, but it wasn't what it could have been. I allowed it, though. We would spend hours doing little, detailed cleaning up on Paul's songs, but when it came to mine... especially a great song like 'Strawberry Fields' or 'Across the Universe' ...somehow an atmosphere of looseness and experimentation would come up."