[benkan]

Note: I am a product manager myself I see the team of PM, Engineer, Design, Data, etc. as one team consisting of people with different skills. The skillset of a PM does not include coding, but it helps to have some technical understanding to discuss on eye level. The skillset of a software developer does not include user understanding (for example), but it helps to have some idea of user situation to discuss on eye level. If all functions understand what the others do, the team will be successful.

In my opinion, your experience of product managers sounds like people with poor understanding both of the job of a dev and of the job of a PM. No blame.