Expecting your senior engineers to be producing like exponentially or even linearly more work is not utilizing those engineers' expertise correctly, especially at a startup, in my opinion.

Seniors and especially higher should be expected to be spending some amount of their time on mentorship, helping others, creating/advancing product initiatives by planning or coordinating. If your product managers are flying solo with no input or even having non-technical managers dictate, that's worse than pulling seniors into some planning.

I've never had someone lay this out for me but my experience is there is a large chasm between senior and higher. Bridging that chasm generally doesn't come with increased individual technical output, it comes with utilizing others to advance projects with you.

That isn't to say senior+ can have no technical output all the time but I wouldn't be demo-ing an engineering RFC or new engineering initiatives at a demo day which will be consumed by other teams. Demo days aren't for the engineers or even product team; they already know what they did that week, I can go into version control or listen at standup.