That's a weird perspective to me, personally. I don't view seeing someone in a different environment or from a different perspective as seeing a different person, just as seeing a different side of the same person. It expands their character depth. Unless it's explicitly an alternate universe or timeline, of course.
On that note, as for how linked CS and Firebreak are, they've said that they intend to try to import world state variables from CS into Firebreak. So it's intended to be a sequel unambiguously.
I doubt CS MC, Jaye, and Mal will have significant presence though, even if they have cameos. They've had their time in the spotlight and hopefully their HEA. And the epilogues show them not being heavily involved in the Firebreak project.