Of course, to realize their potential they also had to work hard, and collaborating with other exceptionally talented artists also no doubt helped.
I would also push back on the idea that the music they created as a group was much better than what came after. George, in particular, released arguably his best work (all things must pass) after the breakup, and both john and paul released great albums afterward (imagine, ram)
That said: All Things Must Pass is unquestionably George's best work and the overall best Beatle solo album. But I'd argue that every other solo album was considerably less interesting than, say, Abbey Road or Revolver. Imagine has two classics, some interesting stuff, and some filler.
Scene starts at 1h02 in Part 1. His talent is depressing.
That's just an absolutely crazy amount of hours to be performing in such a short period of time, and nearly impossible for most musicians to actually get paid for (outside of relentless busking).
I think very few bands since have worked as hard as the Beatles. Their 2 years in Hamburg playing long hours in night clubs daily is something few bands can do (or would want to), and that forged them into something special (not just in technical musicmanship). The Beatles never shied from putting in the work.
Other 'factors of the time'. They wanted to play rock and roll. There just wasn't THAT MUCH of it. In 1961... there were a few years of the genre, several albums by their heroes, but... it's not enough to play and attract people in bars for weeks on end. There were other factors too, but that constraint was one, that helped push them to expand a bit beyond just 'rock' stuff (some earlier standards, etc) to help differentiate themselves from other bands (and eventually self-composing as well).
By coming back from... IIRC, their second or third Hamburg stint, they had somewhere around 800 hours of playing together as a band. That just wasn't a thing (yet). I mean - not even most of their heroes/idols didn't have that much stage time as a single unit. The "self-contained rock band" really wasn't a "thing" yet.
I've been in bands, and we were never even in a position where we'd be able to play 6-7 hrs a night for weeks on end. I'm sure no one would have wanted to anyway (like you say).
"Like the Beatles" how?
They were at the right place at the right time (that is, the time where pop music was starting, hence you had less granularity), and singing in the "correct" language to get a massive audience.
Further than that, they were lucky to not get broken up or faded out early.
This in no way diminishes their work, but it was a hole in one.
In a way it's kinda of a Fermi paradox of bands, except there's no paradox because nowadays there are multiple bands (at smaller niches) with several very competent musicians playing. Or "manufacturing" bands.
Is Max Martin a lesser musician than Paul or John? Probably not really and I don't like most of his songs.
It's unsurprising that the Beatles' music they created as a group was better than what they did afterwards (much better). After all, if you're John Lennon, who is going to tell you your latest song sux, and btw, here's an improvement to it? Nobody but a fellow Beatle.