Yes. Date of hire is irrelevant once you establish position on your respective seniority list. I'm assuming hypothetical 2000 hire at Southwest is an F/O because he can't hold captain at his respective company. If that is the case, he made the choice to go to a carrier that had slower upgrade. Disclosure- I don't work at either airline, but have been through a seniority integration.
And you made a choice to go to stepping stone carrier that got bought by a stonger carrier. That was your decision. So why should SWA pilots have to pay for your poor decision making?