I have been flying them pretty regularly for 10 years, including during and after bankruptcy, and I haven't seen any changes because of it. In the 10 years, I have seen improvement - newer planes, better boarding experience. The criticisms are valid - they suck at refunds. Beyond a simple delay, they often seem to lack any authority/initiative. I have never been downgraded, so I can't speak to that.

I will say that all in all I don't usually have any problems with them. Routine delays are not uncommon, especially dealing with MEX. But I don't think they are a bad airline.