Well, as a long-suffering Torontonian, I can't say I'm familiar with this "only watch the Leafs" culture.
So I probably don't qualify as a Leafs fan. I do cheer for the Leafs (hopeless as it has been the last 30+ years of my life
). But I watch other teams, and I cheer for them in the 'Leafless' playoffs. Only time I've cheered against the Leafs is if they are mathematically eliminated from playoff contention and their opponent is a team I like and they need the points.