Why do you think John was so negatively obsessed with Paul? If his incessant mentions of him in his diary are true. And almost all in tone are erm disparaging to say the least lol It kind of contrasts his more casual remarks about him to others (usually an acknowledgment of their history together and affirmation of their separate lives). Perhaps the acrimonious financial mess was enough of a pain to leave a lasting bitterness in John where Paul was concerned? Sometimes I think because their relationship was characterized by competition that John couldn’t help but continue to measure himself against Paul to the point where it wasn’t actually about Paul and more John using him as a proxy for all the ‘bad things’ (sort of a mirror to Yoko being a proxy for everything ‘good’). Idk it seems like Paul’s innate enthusiasm and confidence was why he and John became fast friends but tbh even without the band it seems like John and Paul were always kind of bound to be adults with very little in common aside from the same love of music.
On the whole, I do agree with you concerning Paul becoming a proxy for "bad things" (and the above ask elaborates on why Paul was that person).
I'm not sure I agree with you on John and Paul being bound to be adults with very little in common. I think Paul found John's interest in the occult off-putting and difficult to navigate, but I don't think that was always going to be as pronounced as it ended up under Yoko's influence. And as elaborated above, I agree with you that John was negatively fixated on Paul to the detriment of their relationship, and while that would have been difficult to resolve, I don't think it was impossible.
I also struggle with the idea they necessarily needed to have more in common than their love of music to be friends – that's already a lot IMO! And clearly they always shared a sense of humour and were able to have conversations about bread and babies. I know some think that was worthless, but tbh, a lot of parent-aged adults like talking about what they cook and their kids.