PMs also need to have a fair idea about the business aspect of development, after all we are all making stuff to sell. So if the designer/developer doesn’t understand that, this doesn’t hold true.
Also, PMs may be needed in slightly bigger startups to not just direct, but also get fresh ideas. New hiring isn’t always bad. Onboarding is definitely essential.
Failing initial employees is a case where the employees feel they could have done without the PMs. Maybe, every developer/designer thinks that way, because the job of a PM looks like extended common sense. But let’s face it, common sense doesn’t appeal to everyone after all :D