There are lots of protections. It goes WAY beyond pay, work rules, benefits, etc., but having that in a legally binding contract is imperative. It means having a barrier between you and both management and the FAA if something goes wrong. It means having access to additional disability insurance. And it's contributing to the advocacy for safety and protection of our jobs. SkyWest pilots reap all the benefits that ALPA has delivered over the decades (safety advances, fatigue rules and programs, KCM, etc.) without contributing anything. I consider it a form of theft.
Republic and Gojet are both Teamsters, so they at least participate in representation and the Teamsters have a long-existing airline division.
Also, Republics upgrade is pretty quick at 2.5 years, but your first upgrade opportunity will be LGA or EWR. The 5 year figure is to hold CA in ORD.