That’s not accurate at all, you only need a simple majority in parliament to pass either mixed-member proportional or the single transferable vote electoral systems.
It’s only with the party lists that transcend provincial boundaries that require a constitutional amendment. Though no one is pushing for that system as we want to keep our local representation.
It needs to pass 3 readings in the house, 3 readings in the Senate, and likely has to face the 7:50 rule (7 provinces representing 50% of the population).
In his first term, he had the house and not the Senate. In his second and third, he didn't even have the house (and the Senate situation would be nebulous now as well). And they'd have always struggled on 7:50.
His real regret is not putting it forward and letting his opponents vote against it.
All that said, even an incremental improvement, like decoupling the leadership vote from the MPs/MLAs would have helped a lot with getting rid of a lot of our worst MPs/MLAs; not all of them, but baby steps to making all the parties healthier (including our the ones most beholden to their crazy factions).