This is sort of true and sort of not. FAA initiatives are applied evenly, but airlines can propose substitutions, and UA has a reputation for subbing in mainline and out UX flights, which makes sense to me, help more customers. Most other airlines have mainline and regional completely independent so that doesn't happen (and how UA manages to coordinate them, given that the UX airlines are operated by different companies in different locations, is surprising to say the least; could be it's another one of those unsubstantiated rumors).

The FAA is trying to go to fewer ground stops, replacing them with other tactics like specific flow-constrained enroute areas to avoid, etc. Ground stops make sense when they're truly airport based, but historically they have been mis-used when some nearby airspace is a problem and they had no better tool to handle it. It will be interesting to see if there's any improvement this summer.