My understanding is advancement at FlexJet is purely "Merit" based since they dumped the union. "Merit" being a nice way of saying "A-Teamer", "Team Player", "Company Leg Humper", etc. Seniority pays little to no role in it.

Disclaimer: I have not worked for FlexJet (I'm NJA) but have talked to a number of their pilots and read the stuff they've posted on this forum for the past few years.