There’s nothing like comparing apples with shock absorbers is there?
The whole LCC model is the “teaser” rate, but then when you add the basic level amenities, it soon starts to add up. Frontier will hit you with a personal item fee, choosing a seat fee (anything from $20 to $60), early boarding fee etc, etc. Now if you book Delta basic you will also get a bare bones service and pay for a bunch of stuff, but depending on how much you want to relive the Roman galley experience (Frontier has less beatings but more shouting), you may want to avoid LCCs. If you can put up with it and need to save money, then good for you, but nobody is getting on that flight for 29 bucks.