From the perspective of someone that lives in YYJ, there is a place for Westjet in my travels. But it isn't very big.
They offer non-stop flights that AC does not, so when my travels take me to YLW, YEG, and now, YYC, I'll pick WS over a connection.
Having said that, their YEG & YLW schedules are pretty weak, so when their non-stop doesn't work I usually end up booking AC via YVR (but, never WS with a connection).

Sometimes WS is also the only choice for a domestic connect when booking with an international carrier. Some WS flying sneaks in for me that way, too. For instance, this year I had an AA itinerary that could only be ticketed with WS on the domestic leg. And same for Icelandair last year.

But really, I never seem to have a great experience. Their tech isn't great. They have some customer unfriendly policies that AC does better on (such as ability to choose a seat at time of check in on basic fares). There's the contract staff issue that's been brought up before repeatedly. And they've forgotten how to run a reliable operation. Outside of flight schedule, there're really no competitive advantage that makes me want to choose WS. With their network here, it would be easy enough to consolidate all my flying with them. But they don't compel me to do that. In fact, it's the exact opposite - they repel me at each contact point.