Agreed, JB. For all Shatner's faults, I think he nailed the truth when he said that the supporting cast began to retroactively delude themselves that the original show was planned as an ensemble cast, a la TNG. Not helped - as he pointed out - by the adoration at conventions. I think it particularly went to Takei's head, with his pushing for a CAPTAIN SULU series, even though I think he is actually fairly limited as an actor. (Nick Meyer dragged greatness out of him for a few seconds in UNDISCOVERED COUNTRY, but I thought he was awful in the FLASHBACK episode of VOYAGER, with what I saw as his faults on view.)
So yes, I think the dislike of Shatner was perhaps always there, but hidden behind forced jollity, hence the seemingly good times on the mistake tapes, but that whatever resentments their were got magnified out of all proportion when TREK became a phenomenon and the cast suddenly felt cheated.
In her book, BEYOND UHURA, Nichelle quoted (roughly) this....
SHATNER: Well, we all laughed and joked....
NICHELLE: No, Bill! You laughed and joked. And everybody else just went along....
Walter - at least - had the honesty to admit to him that they, the cast, were partially responsible for all the misery, because not one of them had ever dared confront him, due to fear of getting discreetly chucked off the show.
Walter wryly says in his book that the consequences from the fear of power are perhaps sometimes worse than actually just confronting the power itself, because he will now never know if Shatner would have backed down or not in his selfish behaviour.