A & B have been discounting at those levels long before the C-Series came along. It's true the C-Series bringing the GTF engine forced A & B's hand to refresh their offerings.
The C-Series problem isn't the plane, it's the financing and the cloud over BBD's future. Everyone is absolutely sure the B737/A320 will have a resale market in 2023, that can't be said of the C. BBD is fighting a huge installed base and support system versus some real after delivery support questions. When CRJ F/Os complain about BBD support, you can bet there's a problem.
GF