If that’s the case my honest advice would be to stay at your regional for a few more months, learn, soak 121 flyn up like a sponge, go through a full winter season of crappy weather, deicing and such (perhaps even part of a negotiation cycle) at the same time apply directly to the legacies if that’s where you want to end up. It would make you a far more rounded and appreciated member of whatever team you’d end up with. Jumping from your regional to JB to legacy (these days) is a wasted step and effort in between for all involved. You don’t learn 121 ops in the schoolhouse (thats where you learn the basics of the plane and jargon like 3585 which u memorize but never apply nor understand)…. You learn on the line as you get comfortable and actually know what’s going on at a deeper level, that takes experience which takes time in one place.