They had two overtly political songs that I can think of Taxman and Revolution. Both are quite good songs, I don't really wish for more and I don't get any perception that they were that politically savvy. Blackbird was conceived as a political song, but even knowing that it doesn't really strike me as one.
I pretty much agree with Kyle's assessment of Paul re 911 it was facile. I quite like Paul's looking for Changes, partly because it shows a sincerity (or maybe it's more a willingness to put himself on the line) that is often lacking in Paul, but also partly because he doesn't usually do that.
As artists they were speaking to inspiration and the human condition. Imagine I think was John's most successful political song, I think primarily because it was a vision piece.
Still Ian MacDonald called his book on the Beatles "Revolution in the Head" and I think that reflects in a way that the Beatles caused some sort of cultural revolution, not necessarily all for the better.