Greater than the sum of their parts. George Martin deserves credit for reigning them in.
The band disentigrated before their pet projects overtook the legacy of the band. Nothing that they have done in the decades since has matched the merit of the "group's" works.
That legacy is what kept them from mucking about with ANY thought to reunions (with or without John). I can accept that they reunited for Linda's funeral and I am glad that was not filmed and released to the networks for round the clock coverage.
If the Beatles had remained a band, we could have expected more 2 record sets like The White Album with essentially a side of cuts from each member (they all wanted to have "their" songs represented on the albums).
The 70s sucked anyway. Better for them to snuff out as a band on the eve of that decade than to go disco, country, singer/songwriter, party band, or prog.
There will never be another "Beatles" for better or for worse. There may be the same amount of hype for a performer for 2 years but the music won't have the same worth and few artists release that many original songs in a year (there are some but they don't get radio/tv exposure). Any more, it seems to be 2-5 years between albums. The Beatles would never have lasted long enough to put out all their albums at that rate; imagine only hearing every 3rd Beatles album and trying to figure out how they got from A Hard Day's Night to Sgt. Pepper's? This is the way it is today with some bands (local and national) who find album after album shelved (because of delays at the label or changes in band lineup) meaning that much of the evolution of the band's sound is not "documented" leaving the casual listener unable to accept the change in a performer's sound.
The last paragraph sums it up quite well, weegee. While I do think they're far overrated I have to agree with your assessment. There will never be "another" Beatles for many reasons. The "system" just won't allow it for all the reasons you mentioned.
A list of great albums from the 70's would run in the hundreds. .....by The Rolling Stones, The Who, The Kinks, Pink Floyd, Led Zeppelin, Bob Dylan, Neil Young, Little Feat, Jethro Tull, Bob Marley, Tom Petty, Elvis Costello, Tom Waits, Frank Zappa, Lynyrd Skynyrd, Leon Russell. .....too many to name.