So as far as fans go, I'm one of the least well-read about technical details so please school me if I've gotten it wrong!
Personally, I consider George Martin to be an essential part of The Beatles. Maybe not the "Fifth Beatle", but he was an integral part of their success (talking real-life here, because no one can say how the band's career would have gone without him)!
They had raw talent in spades, for sure. George Martin was just particularly adept at polishing it and giving it direction when needed. Strawberry Fields is a good example of GM's wizardry, combining two different takes, two different tempos and two different keys into one hit. Think about Let It Be - Phil Spektor produced that one, and to me it just doesn't work as well as the Martin-produced records.
It's all a matter of opinion, but I guess what I'm trying to say is that I think George was the right guy for that band, anyone else and they wouldn't have been The Beatles as we know them. And we all know that Paul and John have/had big egos lol