Even if it were true that no overlap could have occurred between the cohorts and the pricing/existence of the AB product has no externalities upon the PD product, it's not "fine." It’s a total ripoff by a company that's supposed to be their partner.
But Amazon is not their partner.
They are a reseller and like resellers have done since the beginning of time they will take the opportunity to cut you out if your product is successful and it's profitable for them to do so.
Amazon is one of Peak
Design's biggest partners.
Amazonbasics is just the generic version of much of the overpriced junk they sell. The only people being ripped off are the ones buying the name brand versions.
Amazon is certainly allowed to make their own bags that fulfill the same function as PD's bags. What they're not allowed to do is to copy a design without permission.