Here's a simplified version of the story.

I had YWG-YQR-YWG-YYZ booked.

It booked as YWG-YQR fare in S, and YQR-YWG-YYZ in V, because YQR-YWG only had V available, but YWG-YYZ is wide open.

They cancelled YWG-YQR, so I can't possibly take the YQR-YWG, and thus, I'm changing the ticket to YWG-YYZ.

They're willing to give me a refund of the difference, but they refuse to put YWG-YYZ in G (which was and is available), because the original ticket was in V.

How hard should I fight on this? On the actual ticket, I'm looking at somewhere between a $100-$200 refund.

My thinking is that I didn't buy V because I wanted V, I bought V because YQR-YWG forced me to. Now they can't fly me to YQR (and therefore back), so it doesn't make sense to force me to pay for V when all I want is lowest Flex.