Seat pitch on an Encore Q400 is 30" or 31" depending on the seat. Rouge is 29".
Beyond that, the rouge seats are hands-down the most uncomfortable of any I've ever experienced in over 40 years of flying. An hour in and both my butt and my back are positively screaming.
I guess the third consideration - and the one that nails it for me - is that at least the Westjet plane will arrive on time more likely than not. Air Canada - rouge included - is very well known for having the worst on-time performance of any airline in North America, and ranks among the absolute worst in the world. I don't want to sit in that rouge seat for one moment longer than absolutely necessary, so having a two-hour flight become a three-hour ordeal or a four-hour ordeal because they can't get their act together just make a brutal experience that much worse.
When I need to fly YYZ-YYG in the winter when WS is on a reduced schedule, I regularly route through YQM on WS and drive from there rather than fly direct on rouge. Yes, it really is that bad.