Well, his career as a solo artist wasn't an overwhelming success, he actually spent much of his post-Beatles life as a film producer.
I don't think he would have been anywhere near as successful as the Beatles, and I say that with having no idea if he could write enough hit songs to top the chart. Say he wanted to be his own front man, and not the Jimmy Page boss-man of a band that had someone else singing... his singing voice was weak, and his personality was never hugely appealing to the public, except as the Mystic Beatle when mysticism became fashionable. That was one of the secrets of the Beatles success, not just that they were a kick-ass band and some of the best songwriters ever, their personalities were hugely appealing. Ever since, cynical producers have been trying to assemble boy bands that had a cute one like Paul, and a fun clever one like John, and a sweet one like Ringo. I mean I always found George's sardonic humor appealing, but not everyone does.
I still think Harrison's best bet as a non-Beatle would have been as the guitar player and songwriter in another band - he was a terrific guitar player and songwriter, but he wasn't born to be a front man. He didn't have a great singing voice, and I don't think he ever had the kind of big personality that reached out from the stage and grabbed the audience.
But then, none of the Beatles did, as a solo act, it was the mix that worked.
Irrelevant to the issue though. I'm not saying the guy didn't have talent. I'm saying he would never have succeeded without his association with Lennon & McCarthy. They made The Beatles. You called all three hacks anyway.
Or you could just look it up. Harrison's first album after the Beatles "All Things Must Pass," hit No. 1 in the UK for 8 weeks, and No. 1 in the USA for 7 weeks, easily outpacing the first solo albums from Lennon and McCartney, and was critically acclaimed. He also had 3 number one solo hits after the Beatles. ("My Sweet Lord," "Give Me Love (Give Me Peace on Earth)," and "I've Got My Mind Set on You")
Harrison also teamed up with fellow rock legends Bob Dylan, Tom Petty, Jeff Lynne (of ELO fame) and Roy Orbison to form The Traveling Wilburys, a supergroup with two platinum albums.
Yes, "ATMP" was a huge hit, and Harrison had solo singles, but his musical career slowed down during the 1970s and none of his subsequent solo albums were as successful as the first. By 1980 he was considered a has-been as a musician, and was starting his second career as a film producer.
A man of many talents, and he was successful enough as a film producer that some people have said "He saved the British film industry", but as a front man... he was no Mick Jagger? So really, if he'd never joined the Beatles, he'd have been better off finding a Robert Plant for his band than being the frontman himself.
No, his solo career was centered around Hare Krishna. Too religious and special interest to attract mass appeal. He never would have been given that platform without John & Paul.