In all seriousness it was probably when Claremont left, in a lot of ways. Under Claremont’s pen he was allowed to age and to be a character, and his role was that of the elder statesman with the mysterious past, the occasional killer with the sweet side, who was always nursing some nagging injury and fretting about being past his prime. Now he’s forever in his prime, the mysterious past is gone, the sweet side comes and goes, and his feats are ever-more outrageous. This is what happens when he shifts from being on a narrative path to being an eternal property, and it happens to all company-owned characters eventually.
At the same time I was not joking about the smoking thing—that really exemplified that he is no longer a character but more of a corporate mascot, which is a move that some characters survive (Batman, Spider-Man) while others do not (Superman, Hulk).
That was the beginning of the end of the whole Marvel comics line. There have been some very good books since but by and large, the line has been a turgid mess since that title debuted, often as a direct result of that title’s influence.