Your discussion of the reluctance of caucuses these days to push back against their leaders is well-put. That said, over the last couple of decades I've seen a phenomenon I call 'Pop Goes The Premier'. Multiple Alberta premiers, from Ralph Klein to Ed Stelmach to Allison Redford to Jason Kenney, have all been 'convinced' to leave by their caucuses when the MLAs started to think the public were souring on them. The funny thing is that Stelmach, Redford and Kenney had all scored decisive election wins, but they decided to resign rather than face the voters a second time. They didn't resign due to formal caucus revolts, but they all saw the writing on the wall.
Indeed, Alberta conservative MLAs have been notably active in undermining their leaders, as part of longstanding ideological rivalries within their party. As you say, none of these premiers was formally removed by caucus. Neither, in the formal sense, was Mackenzie Bowell.
But the really vital question in a parliamentary system is not how a leader is removed but who can choose the next premier.
Charles Tupper, Bowell's successor as Conservative leader and prime minister, was chosen by the same parliamentary caucus (cabinet, MPs, senators) that had withdrawn its support from Bowell. The process of 1896 (both in removing and replacing Bowell) preserved the fundamental principle of parliamentary democracy: a premier's right to hold office is conditional on having and holding the ongoing support of the parliamentary majority.
All the Alberta premiers, by contrast, came to power in their party by winning mass-membership vote-buying contests. Some of them, Alison Redford most notably, had little or no caucus support from the start. And all of them were replaced by new leaders chosen by the same kind of extra-parliamentary contests, and therefore came to power under the widely-held assumption that they had no real accountability to the majority of the people's elected representatives in the legislature.
Alberta might one day be the place to revive parliamentary government in Canada. But the disputatious backbenchers would have to take the essential next step and assert their authority to chose a new leader clearly accountable to them, to replace the one from whom they had withdrawn their confidence.
No sign of that, however.
