Product Managers today are many times attempting to be shitty tech leads rather than actual product managers, which is a completely different job. If a product manager has more than a superficial opinion about what engineering is doing, then they are not a product manager (more than by title). They should feed the why and when to engineering, nothing more. When do the market opportunities exist and why? Collect and feed the data to engineering (as well as other stakeholders). They should not be the customer proxy, not lead engineering teams, nor be some go-to person for "final decisions" on design matters.