Yes, it is one route and as you say, a core route. So being at the WN core it should be a very competitive route between WN and DL; indeed, they both have lots of nonstop service. Yet Delta costs 70% more for last minute tickets, while offering connecting last minute tickets from upline cities with the same ATL-TPA segments at heavy discounts. (Again, I am saying this NOT to start the hidden city or fortress-hub-is-higher conversations, but to dispel the feeling that every Delta flight was chock full.)

Other posts have wondered if this was a weird situation, time of day, etc. I checked the same pattern for tomorrow and it is identical. Same fares on WN all day. Same fares on DL all day -- and 70% higher except a 300% bump on the last flight at night. I will check it a few more times in the coming days.

WN does not serve MIA, ORD, DFW or IAH and NYC is a collection of airports, so not the best comparisons although I agree something could be made of comparisons between airports in the same cities, etc.

But DEN seems like a good comparison-- a legacy hub vs. a WN focal point or whatever they call their big locations. I have only checked United for tomorrow against WN for three larger cities at a medium distance. Two have been traditional strong points for WN, just as TPA is now -- Albuquerque and Salt Lake. I also checked Kansas City, which is these two carriers competing between two "hubs" (it is is a somewhat different case, therefore).

For tomorrow, last minute ticketing:

UA DEN-ABQ $220 OW 4 nonstops
WN DEN-ABQ $221 OW 3 nonstops

UA DEN-SLC $208 OW up to $615 OW 4 nonstops
WN DEN-SLC $209 OW 6 nonstops

UA DEN-MCI $317 OW 5 nonstops
WN DEN-MCI $335 OW 5 nonstops

I didn't cherry pick these but my flight to Tampa leaves in a while so it will have to do for now. The Salt Lake example was interesting -- UA matches WN until the evening, when WN is sold out -- then they triple the fare for their last flight, which is an RJ. A nice touch, but at least it shows active, competitive pricing in the marketplace.