Jimmy's is super overrated, I 100% agree.
Calgary does a pretty bad job of Donairs, to be honest. At least compared to Edmonton. I'm partial to an actual Donair, sweet sauce needed, and Calgary relies on a garlic blend too much and it's just shawarma.
Big Johns and Blowers Grafton both do an actual donair (Halifax style). Those two are my favourites. There's also a Donair food truck that's downtown during the summer, but it's expensive as **** and maybe the size of a hot dog.
There used to be a place near Sir Winston Churchill High School, in the professional strip mall next to it that had donairs that tasted just like Swiss, but it's gone now.
Calgary sucks.