Any musician in a band knows that the main studio room is off limits to non-band members when recording. The control room is up to the engineer as well as the band, but that's an appropriate place for a girlfriend, parent, friend, whomever.
The very clear footage of Yoko sitting in on the Beatles recording sessions is OBVIOUSLY uncomfortable and anti-creative. It may have been Lennon's response to McCartney's control at times, since McCartney was the more socially acceptable, and Lennon was the real rebel. It's likely Lennon/McCartney would've split before long, headed towards 30, and the late 20s being a very emotionally volatile time, but Yoko being in the room with four guys who owned the world did not help.
To me, its amazing that either McCartney or Herrison stood for it at all, but contracts are contracts, and they were seasoned businessmen by then.
Lennon was vulnerable and Yoko manipulative, but they did seem to find lasting happiness. Sure, she helped break them up in a major way, but they were destined to stop before much longer probably, but who knows? A couple of years off, or if Lennon were alive since 1980, we might've gotten some more Beatles records.