I'd disagree. After X thousand hrs in the same airplane, same seat, and the same type of flying, the learning curve flattens out. If there's significant opportunities ahead, CP, CKA, union leadership, I'd stay. Otherwise, IMO, they can push their learning curve and consider long haul international wide body flying.

There are things learned in all forms of aviation. Doing the same thing, again and again, when there are other challenges available, is something the majors are concerned about. Lack of exposure to challenges, or training, is a prognosticator of future training problems.

This isn't a call for irrational, or hard to justify, job hoping. Laterally moves, that don't make sense, will invite additional scrutiny.