Tbh I’d say keep the rack loading as an option or attachment for rule of cool purposes. It’s a slow game with plenty of time to reload and this is way too cool and unique to pass up.
I and many players like weapons that are cool but less powerful, that’s why we use the Revolver, UMP, and other slower weapons that lack attachments and are objective downgrades, they are so cool!
Alternatively you could have the rack loading mechanism for a super shorty shotgun secondary, which would be balanced as a shotgun secondary would be powerful and unique but should have a long reload downside.