Why should not all those be together and be the bar for senior starting at the start-up layer? I think the only big difference is working/navigating in a small or large org, no?
If you look at the both extreme, large public company and a start up, in the former case, you already have customers, a viable business model, and a legacy product. As an engineer, your first requirements would be to "not break things" going forward. Sure you want to gain some market share from competitor but you already have some momentum, otherwise your job would not exist. So you need to upgrade or add features to your product in a controlled way. Your 20 years customer might not want to have to learn a new interface just because you can deliver it.
At a start up, even if you have your first customers, you want to deliver a product or more features as quickly as possible starting from scratch. Possibly, you also want to be able to pivot totally if the first idea does not stick.
It is great if you can do well in both environment, but usually, this is different skill set, and I would even say personal inclination. You'll likely have a hard time to convince a start up engineer to work on COBOL code base on a mainframe.
