I don't think it's necessary to stay with the same company a very long time to develop "deep knowledge". on my last team there were two engineers with about 20

I don't think it's necessary to stay with the same company a very long time to develop "deep knowledge". on my last team there were two engineers with about 20 years of experience. one had spent all of it at that company, and the other had worked at five different companies in the same space. the former knew more about the company's code and was an invaluable resource for "why are things the way they are?" type questions. but the latter often proposed more novel (to us) solutions, drawing on his experience from previous roles. both were extremely effective engineers.