Frontier may have lower pay rates but growing faster (we are slow growing and SLOWING GROWING (read that until you understand that)).

Faster growing at Frontier equals better seniority, faster natural upgrades (vs upgrade due to bypasses that leave you on reserve forever) and also remember that everyone at Frontier is on Airbus pay vs awful E190 pay (lower than 99% of other major airline pilots).

I agree with the other dude, you probably can't not take the JB class date, but keep working on better opportunities.