Don't usually comment on anything other than Stuart, but since I also read Fred Seaman's book as well as the very interesting "Get Back: the Unauthorized Chronicle of the Beatles Let It Be Disaster", I'll share my somewhat ambiguous Ono opinion. I gotta say I definitely agree with Casbah---well said indeed. I'll add that I think, bright as Lennon was, he was a pretty lazy guy---and was easily led and influenced. Stuart was the dedicated, impassioned artist who showed John how to paint when the art school profs couldn't make a dent; McCartney was often the advocate of new, unconventional music and musicians; there was the Maharishi, Magic Alex, Allan Klein and of course, Yoko herself to lead and beguile. Once interested and the groundwork laid, John would throw in with all he had...until the next new thing came along.
I don't think Ono broke up the Beatles. In my opinion, the band's breakup was inevitable from the start, caused by the personalities and behavior of its members. Not that Ono didn't use that for her own benefit.
Having said all that, I also think that Ono's poetry and early performance pieces (the voiceless ones) were intriguing and worth attention. They weren't getting enough attention, apparently...a world-famous collaborator (especially one easy to manipulate) would certainly boost her celebrity. And once John became a martyr, her name was was assured.
"Love" is a word that covers all sorts of needs and motivations. John needed Ono at a time when everything he used to believe in was slipping away. It's my personal opinion that had John lived, he might have found himself enough to detach from Ono. He said he was "starting over"; hopefully that effort would have seen him "moving on".