No it isn’t. He left because he challenged Morrissey about letting good people go ie Gaz. Alain is quoted as saying that he left because of why Johnny left.
This is very confusingly worded. I'm not aware that Alain ever compared his leaving to Johnny, though I'm happy to be proven otherwise. Johnny announced his departure to the press, outright. Alain - or, for that matter, Morrissey - never said anything publicly before the mentions in
Autobiography. Which, frankly, given his impulses to embellish a good story, should be taken with a large salt lick. For instance, he claimed that Alain had legally asked to have his face put on the cover of
YATQ whereas I'm inclined to envision the reality being akin to a request to have a larger font size credit - e.g., Songs by Morrissey & Alain Whyte (with an asterisk or some such for the Boz/Gaz co-writes). Given how the bulk of that comeback was on the shoulders of Alain's material - again, all four singles were his co-write and ultimately all became UK top 10s - it would not be the most unreasonable ask after years of carrying the bulk of the songwriting duties.
Also, Gary did not leave until after the completion of the
Ringleader tours which Alain was not asked to participate in. At the time, he had been working hard to launch Red Lightning. Alain also submitted the songs for
Years of Refusal circa 2007 after Gary had been replaced by Solomon. The long hiatus between then and his return to touring in 2021 was apparently prompted by being barred from participating in the sessions for
YOR as he had on
Ringleader. Allegedly (apocryphally?) Boz was tasked with dismissing him in the recording studio parking lot.
There's a lot we'll likely never know. For their own reasons they've both decided to share what they're willing to share (M through his book, Alain through podcast interviews). For that matter, I don't believe it's ever been clarified if M ever reached out for new songs in the post-
YOR era or if they truly cut ties for several years. I always got the impression that they had both arrived at the conclusion, mutually if separately, to carry on in their own lanes.