Every company has different risks, and so every company expects something different from their senior engineers. An engineer who has spent the last five years making small, continuous improvements to the processes in a larger company may not enjoy or even understand the sort of role expected by a three person startup. The expectation that “senior” is a fungible title is both widespread and harmful, leading to unrealistic expectations from both engineers and companies.
Through trial and error, engineers can identify the sorts of problems they enjoy solving. A senior engineer should find a company which both has those problems, and knows it. Anything else will lead to frustration, and eventually apathy.