Does anybody have a credible source discussing flight cancellations on Spirit or Frontier in which passengers were told they’d have to wait several days before they’d be accommodated? I certainly can’t find any.
Sure, I can give you several first hand incidences. We usually only fly Frontier because it flies out of our local tiny airport to MCO, but we've been stranded several times and so have many of our family members. Once they were able to accommodate us the next day when they cancelled our flight. Twice we had to take flights out of a different airport (and then figure out how to get our car since our return trip was to the original airport). Twice we've had to buy tickets on a different airline for the next day when they couldn't accommodate us at all. This has also happened to three different family members. (and this is all post-covid, if I went back any further this post would get too long)
MCO is a Frontier hub so I've had fewer issues flying them out of MCO, but getting into MCO on Frontier can be difficult. I don't book with them when it's a special trip or with people we don't travel with often. And I'd never book them for a cruise.
We still fly them because the crews are decent, the airport is 10 minutes from our house, and the price is right, but we do it knowing how often we've been burned. And since the only return flight is late at night we always book the hotel room for an extra night in case the flight is cancelled and we need someplace to stay. At least we get to use the room during the day.
This isn't fear mongering. It's more like being an informed consumer. Long delays and cancellations happen pretty regularly and Frontier is less equipped to handle them than the legacy airlines. There's no one to call, lines at the airport are always long and they charge you for talking to an agent, and the flight schedule is razor thin in a lot of markets.
RE: ground boarding -- Our airport has always boarded from the ground but they have ramps not stairs. They wheel people who need assistance up first and then everyone else boards. They use two ramps, front and back, and I find it nicer/faster assuming it isn't raining.