ATMP was utterly overrated. A triple album I could cut down to 3 songs. Even My Sweet Lord, great as it was, was 'unconsciously' (at least) plagiarized from The Chiffons' He's So Fine. Anything original Harrison wrote that deserved to get on a Beatles album at the time did. George Martin had an ear for the good stuff. And more.._ you could easily let While my guitar gently weeps be the only Harrison track allowed on The White Album and the album'd feel sharper and more fun.
Although he never acknowledged it, particularly when it would have been unseemly to as a Hari Krishna, Harrison thrived on competition. He thrived on having someone say 'write something better or something so polished that it can't be ignored'. I am a passionate fan of the quirky beauty of I Want To Tell You, Love You To, Within You Without You and Blue Jay Way on as equal a basis as Taxman, Something and Here Comes The Sun (and those last 2 tracks, as popular as they are, are really just McCartneyesque anyway. They're like Harrison's take on Yesterday and Good Day Sunshine). But inbetween Revolver and Abbey Road, he was polishing just a few diamonds. For me, his greatest achievement in Beatles terms was to get Taxman as the opening song on Revolver. Because the song was also distinctly the real Harrison - that is, Lennon-like caustic wit and concern about getting ripped off with money , because having a certain amount of money gives you more freedom , as you get older, freedom he treasured to live in Friar Park, as beautifully eccentric a place as some of Harrison's chord changes were deliberately eccentric.
Got My Mind Set On You was a cover. So, for me, it took 20 years for Harrison to get his former songwriting groove back in public when he wrote Handle with Care for his supergroup (and it was) The Travelling Wilburys. The Beatles without Harrison? I don't think Lennon would have felt the need to be so hippyishly cool as Harrison had a coolly mysterious look. The Beatles might have never felt the need to go to India or to have many Byrds-like folksy touches. Therefore , who knows, perhaps without Harrison, perhaps no Norwegian Wood, perhaps no I'm Only Sleeping, perhaps no Tomorrow Never Knows. We might have still had the Lewis Carroll-like Lucy in the sky and I am the walrus and the anthem-like All You Need Is Love but, without Harrison, I am sensing that The Beatles would be regarded now as more straight rock n rollers with a few avante garde tastes. They'd be regarded as more a specifically double act perhaps, like The Kinks or The Hollies. Without Harrison, The Small Faces'd probably got more rightful acclaim.

I don't think I could possibly disagree more.
In my opinion, All Things Must Pass shows two things:
First, George was an amateur songwriter, and Paul and John were right to dismiss him (I'm not sure why you isolated Paul here).
And second, Phil Spector was an expert at over-producing and ruining material. I have George's ATMP album in demo form, and it actually sounded much better before Spector got his hands on it and screwed it all up. He did the same thing with Let It Be. Fortunately, Paul has since re-released Let It Be without all of Spector's crap, and it finally sounds like a proper album for the first time in 40 years.