There is zero chance that in this hiring environment Frontier is going to be able to grow. Right now, Delta/American/United/UPS/FedEx do not have 100% full classes. It would only take a couple months of targeted hiring by the big airlines and Frontier would lose hundreds and hundreds of pilots. Maintaining the same size would be a huge accomplishment, but one that is not likely.
Every month, American/United/Delta will combine to hire over 500 pilots. That is all year long. Every single month. It won't take long to decimate the regionals and ULCCs.
Once all of the regional pilots are cherry picked, the big boys will move on and terrorize the ULCC's by hiring all of their pilots.
Until the ULCC's can compete with the pay, benefits, opportunities, and long term stability that is offered by the legacy airlines, they don't stand a chance to keep their good pilots.