I don't think Trudeau could have whipped up the level of support that Carney did, he lost the "incumbent advantage" long before Trump part dookie. Liberal minority would have been likely out of reach, it would have been a decision between CPC minority or majority. Trudeau was deeply disliked by the time he stepped down, and the polls were continuing to get worse for Trudeau, and as a knock-on, LPC in general.

Carney was able to take advantage of the "new guy effect", and some easy policy changes to attract fence-sitters. I won't disagree that PP said/did some significant foot-gunning, but I don't think that would have been enough to get the LPC out of the Trudeau slump.