I have flown Frontier on a couple dozen flights in the past two years, and honestly I can't remember the last one that was delayed. OTOH, I remember a couple that pushed back quite early because everyone was loaded and ready to go.

It seems to me that everyove loves to mock the poor reliability of Frontier, but at least in my case, the data doesn't support it. (Now I admit that if something does go wrong, you can be screwed!)