How is a HC (who was not fired, just not extended on the terms he wanted) who has a better win/loss record than Sean Payton "bottom of the barrel"?
If the Saints interview McCarthy and prefer to hire a different candidate (Kellen Moore) in the hopes of finding a new gem then that's fine - but I think they are taking a risk. It may or may not be the right move (hindsight is always 20/20). But to me the best indicator of can do is has done, and McCarthy has been a high level HC and OC for his entire career.
Let's see what happens, but I suspect the hire will be McCarthy and that it will turn out to be a pretty good decision relative to the other hires that were available this cycle.