"However, once you get to the airlines it's a whole new game"

I don't see why. The more you bring to the table as a new airline pilot, the better airline pilot you will be. Experience as a CFI makes you a better pilot. Maybe it doesn't help you get through 121 ground school much, or fly a level D sim, but it makes you a better pilot. Which makes you a better airline pilot.

I've been a flight instructor, a scenic tour pilot, and 135 freight pilot, a 121 freight pilot, and a UPS pilot. I've flown Cessna 150's to 767's. I'm just not willing to say the skills to be a good "airline pilot" discount all the great learning experiences one can accumulate as a CFI. Being a well rounded airline pilot means more than just being good at "driving the jet". You learn things as a CFI that make you a better airline pilot. So, it's not really a "whole new game".