I don't think you understand. Under the NLRA, which is where we would fall if the RLA was repealed, the definition of a bargaining unit is quite different. Each domicile at each airline would constitute its own bargaining unit. Furthermore, we would no longer be protected from state "right to work" laws, so domiciles in "right to work" states would have their agency shop provisions disappear. Imagine the Delta ATL domicile having a different union than the Delta DTW domicile, and half of the ATL domicile deciding that they're not going to be members at all, and they don't have to pay dues.
If you want to see how ugly things can get, look to Ryan Air in Europe, where O'Leary has taken advantage of a mish-mash of labor laws and spread crews all over Europe, making it virtually impossible for the employees to organize under a single contract and a single set of labor laws. That's a taste of what we would experience with no RLA.