Someone mentioned there is a discount operator out of Barcelona that goes to Vancouver, but not sure what the schedule is like.Unless Air Canada starts offering flights from Vancouver to Paris, Barcelona, or Rome Calgary would be the best option to get to those cities.
You're point is valid though. Anywhere that Westjet goes to from BC/AB/SK that AC doesn't is going to make Calgary a no-brainer. We have Rome and Paris. I already know people in Vancouver who have taken flights to both those places via Calgary, because it was the best option. It looks to me that Vancouver does not do non-stop to Edinburgh, so that could also be an advantage for Calgary. Change here, or at London? If it were me, I'd rather change here.