Yes and no. Traditionally, B fares ex-Europe (and some other destinations) have been substantially lower than ex-Canada. The lowest B fares ex-Europe generally were much cheaper, but were more restrictive than the ex-Canada B fares, which were more flexible, but generally also more expensive than the lowest Z fare.

Nowadays the difference isn't as large, but I suppose AC decided to keep the restrictions on the ex-Europe B fares.

B fares ex-FRA/LHR to anywhere in NA could be had for ~$2k-$2.2k up until a few years ago. Of course that is what AC is now often charging for the lowest Flex fare.