Paul did in fact bring Linda in on several occasions, perhaps in a game of "if you bring yours, I'll bring mine." Geoff Emerick reports that Yoko was an abrasive, intrusive presence, whereas Linda was so polite and friendly that she was a pleasure to have in the studio. She also shut up and let the fellows do their work, whereas Yoko for some reason thought she was musically competent enough to comment on the Beatles' works in progress. She was an avant-garde artist who claimed she didn't even know who John was when she met him; this gives her musical insight precisely... how?
But Yoko wouldn't have been so intrusive if John hadn't used her to distance himself from the group, which is what he did. He encouraged Yoko to present her views, ignored the others to pay attention to her, and even announced that she would do all his speaking for him. Not the best way to carry on the Beatles, particularly as he could not have failed to notice that the others resented this intrusion into their creative process. I think John wanted to distance himself from the Beatles, and used Yoko to do it. As Yoko was eager to have John all to herself, this was a win-win for the couple and a losing proposition for the rest of the Beatles, whose only choice seemed to be "put up with John and Yoko's antics" or "break up the band".
I wish John had simply said "I'm done now" and walked away from the Beatles cleanly, if that's what he wanted to do. George was eager to be off on his own by then. I wish I had that snippet from some LIB studio tape where George is bringing up, very sensitively, how he'd like to record on his own. Not leave the band! Just... record on his own. They all could do it, but still get back together and do Beatles stuff, too. And Yoko says, "That's a good idea", which made me laugh, because she so obviously wanted to record with John on her own. I don't recall exactly how the conversation ended-- does anyone remember this? I found it on Youtube, but it was taken down. The impression I got was that John was undecided if this was a good idea or not. I think he wanted to keep the Beatles where he and Paul were undisputed top dog, even though he wanted to move in a different direction. I can understand how it would be hard to walk away from that kind of success. It's just sad that they did it anyway, in a far more painful manner than an intentional breakup.