Anyway, what you’re suggesting isn’t that far out. Many bands of the time used session musicians in place of members. The Beach Boys used the Wrecking Crew on some of their albums and on the Byrd’s first single (Mr Tambourine Man) McGuinn was the only member to be allowed to play, with the Wrecking Crew again providing the playing. The Kinks used a session drummer a lot on their first album, including on the singles and were still bringing in session musos playing in place of usual members on Face to Face. The thing is all these details are known. The musicians union in UK at the time was very powerful in the industry and proper documentation of session players was always required. So while these bands didn’t advertise that they’d used session players, anyone who wanted to dig would eventually find the records. In the Beatles case there simply isn’t that documentation to support the idea they used session musicians in place of their own playing (they of course used heaps when hiring orchestras and things). And lots of contrary evidence from the many people who saw them in the studio (engineers and other visitors) and the obsessively detailed biographers they have, such as Mark Lewisohn and Andy Babiuk who delve into all their recordings. We know that Andy White played on Love me Do and PS I Love You on the first album. Due to the studio records we also know that a session drummer was used on the Hard Day’s Night Album - it was engineer Norman Smith who had to quickly do some minor overdubs on Can’t Buy Me Love as the tape had a fault that affected the hi hat sound. The idea that the Beatles used a lot of session players amounts now to a conspiracy theory that would have required the studio’s rigid control from even their earliest recordings. And as if any muso who had done this on a Beatle recording wouldn’t have come forward at some point to claim it. The only one we know of is the Bernard Purdie case which never stacked up and just made him look crazy.
The tape manipulation to make things easier to play probably happened on a couple of occasions. The most famous is George Martin’s piano on In My Life. That was to achieve an effect but also, as Martin admits to, because he couldn’t have played it that fast in real time. They also did the half speed thing to help George on the solo on Hard Day’s Night and I also think on the quick guitar arpeggios on Help, although George did play that fine live not long after. On both these occasions it seems they just wanted to avoid wasting valuable studio time. Aside from that I’m not aware of any other tape manipulations to help them actually play something. There might be some others, I have some vague recollection of maybe a Paul piano part getting the treatment, but there’s no evidence it was that much of a common occurrence. They used tape speed changes mainly as an effect. One of the most famous tape manipulations, on Rain, actually took a faster track and slowed it down. Many people cite this as one of Ringo’s best performances.
I wouldn’t characterise changes in Ringo’s playing as “getting worse”. His drumming changed as the requirements changed. As a live rock drummer in the early 60s he had to play what the song needed. Which he was very good at and why he was an in-demand drummer in Liverpool. One of his most impressive intros on the BBC tapes was on I’m Going to Sit Right Down and Cry, the version on the Star Club tapes from late 1962 is as wild if not more so. He didn’t play like that later in the decade as the songs they recorded didn’t need it. Even then there was impressive if more subtle playing. For example on Here Comes the Sun. As another example of his earlier playing check out his live playing on Long Tall Sally in Washington in 1964 on YouTube.
While Ringo did say he doesn’t like solos and flash, he never said he couldn’t do rolls. George Martin made an offhand comment on that once and it got repeated. Ringo played flashily when the song and audience needed it. The “Ringo couldn’t drum” trope really is the most tired of the Beatle myths that has been buried so many times it deserves its own gravestone.
