I place him as ENTP, though INTP is also possible. "Imagine" is about the most Ne song ever; it's all in the lyrics.
McCartney is a clear ESFP and his songs tend to lyrically resemble Bob Dylan's (ISFP) in that they are almost always about concrete people, things and events, not to mention he's obviously a much more natural performer who's there for the joy of the experience.
John was the one writing songs about broad-sweeping idealistic change and debunking popular myths (like his whole anti-Jesus tirade..."The Beatles are bigger than Jesus!" was classic ENTP pot-stirring.) He also wrote songs like "You're Gonna Lose That Girl", promising to deliberately steal this dude's girlfriend just to make a point/win the game. How hilariously NT. (Granted I could also see an STP doing this, but certainly not SFP...and an STP would be more likely to just DO it, not write a song imagining it...that's so distinctly NTP.)
It's really funny that you'd place Lennon as anything other than NTP especially given his obvious contrast in this area to McCartney, who is SFP as all hell. Note McCartney's total disinterest in political commentary--he just wanted to play music because he loved playing music and that was good enough. Lennon had a clear political and idealistic agenda--that is decidedly not SP.
When McCartney wrote something serious (like say, "Eleanor Rigby"), it was just apolitically humanistic. "All the lonely people, where do they all belong?" Fi all the way.
When Lennon wrote something serious he was making deliberate political commentary to direct and effect changes in societal structure and people's attitudes about it. "But if you go carrying pictures of Chairman Mao, you ain't gonna make with anyone anyhow!" This is clear Ne/Ti sarcasm targeted at a specific political movement to express how dumb he thought its ideals were. How much more NTP can you get?
Lennon was just so ridiculously anti-establishment and focused on massive change and vision for the future...he prided himself on being controversial, forward-thinking, witty/sardonic and above all unique. Talk about NTP!
Anyway the Beatles overall:
Nothing you can sing that can't be sung.
Nothing you can say but you can learn how to play the game
There's nothing you can make that can't be made.
No one you can save that can't be saved.
Nothing you can do but you can learn how to be you
in time - It's easy.