Going to break this down for ya:

Year 1 - $38.50 (Spirit) vs $54 (Allegiant)

You'll unnecessarily accumulate some debt during your first year at Spirit. Some more than others, but certainly some debt when you make 30ish thousand.

Year 2 - $72 (Spirit) vs $96 (Allegiant)

Great! You've gotten back to RJ Captain pay, but no way you're chopping away at that debt that you accumulated.

Year 3 - $77 (Spirit) vs $103 (Allegiant)

Still RJ Captain pay and still not paying down any debt. Man, that $103 sure would help out at this point.

Year 4 - You upgrade. Maybe not for you. You've been here less than a year. But we'll use it anyway.

$131 (Spirit) vs $173 (Allegiant)

Dang, that's a big gap!

Speculate all you want on new contractual pay rates. Chit, speculate all you want on pay credits. These are the numbers that you'll have to work with and average credit hours aren't nearly enough to make up the difference.