Do you have any other prospects on the burner? Can you put off Mesa until you get an asnwer from someone else? You could always start groundcshool then bail in the middle if you get a better offer.

How much flight time do you have?

If you have nothing else lined up and less than 1000 hours, you might want to take it. Worst case stay a year and then you would be marketable to any regional who is hiring.

Mesa is better than being a CFI in most cases, and is certainly better for your career. Also if you live in domicile it's not too bad.