The legacies chipping away at the ULCCs' customers with Economy Basic. The fares are competitive and they'll keep chipping away at ULCCs. The ULCC model is no longer safe and I expect it to fare even worse in a downturn, as legacies will simply increase the number of Economy Basic seats in order to fill the cabins.

I've heard/read the arguments for not jumping ship for a long time. Maybe this time will be different, but jumping ship to a legacy has been the correct move except for short periods of time.