When I've done my flight crawls in just the last few years, off of the top of my head, NYC-LAX, NYC-ATL, NYC-SEA, NYC-LAS, BOS-ORD, NYC-ORD, and NYC-JAX. Since my main base is the NYC airports and four airlines absolutely dominate that market, it's been pretty much every flight I've found where the LCC were more expensive. A sub-$100 RT restricted ticket on many of this city pairs is certainly not unheard of, and $300 for a fully flexible with all of the perks depending on the route. Also of note: a RT into NYC from smaller airports is usually much cheaper on a LCC, while a RT out of NYC is more expensive on a LCC, for the same city pair. You can find similar things happening at ORD/MDW, LAX, and a number of other large O&D markets. Supply and demand at work.
All of the legacies offer them, they may not be on the website or easy to find, but if you call them up or use a travel agent, they have them. You can also book them day of since they're completely unrestricted, and they're the ticket type that the military uses to send service members around under orders when they can't hitch a ride on Air Mobility Command. At least on AA, they also extend the same treatment to any military member in uniform regardless of ticket type and restrictions, and I believe other airlines do as well. The fare code for these tickets is Y.
I personally don't like to fly them, but I do recognize they're a good force in the market and other people do like them quite a bit, and some of my friends and family prefer them, and don't bash people who do prefer them, but I also know the ins and outs of the legacies that many people do not know and are certainly not obvious or well advertised. WN also offers good service to many cities that could not support the operations requirements, including equipment opportunity cost, of one of the three major airlines, and they handle all sorts of destinations that are too big to be EAS, but too small for regular service from the big operators. Especially post-consolidation when we're now down to just 10 airlines with 100 seat or larger aircraft, this is incredibly important.
ATL is an interesting case, because WN picked it up when they bought up FL in 2011. They're doing loss leader flight dumping to try to grab as much O&D traffic from ATL as possible away from DL, which to be fair has a pretty horrific O&D operation there since they're so hub focused, including some of the worst checkpoints I've ever been through, even worse than BOS. ATL is the US' 38th largest city, and certainly doesn't rate attention from DL like it traditionally has had, but it's nearly the perfect size for WN to do much of the O&D traffic. Another interesting tidbit is that as they dumped the former FL 717 aircraft based out of ATL, DL bought almost all of them and they're still based out of ATL, and in many cases this included the crews to fly them.
FWIW, the last time I picked up a $50-ish fare was flying on AA from LHR to JFK, with myself and 12 other people on a 777. The airport fees out of LHR of course brought that to some hundreds, but the fare itself was less than $50.
. I've never heard anyone on the DIS use LCC; budget/no-frills/discount yes (which I think we all kinda understand what that means) but LCC? Nope. Way too technical just because.
