FWIW here's what I got back from their Twitter team. Should be taken with a grain of salt since the policy isn't posted anywhere official.
Baggage allowances depending on the status of Miles&Smiles members continue to be valid regardless of the package selection. If a member with a status prefers the lowest package, the extra baggage allowance will be valid. Thank you.
A bit funny to think of a Classic Plus holder only allowed to check in a 10kg bag.