The point is it shouldn't be allowed for any airline to just change the callsign associated with a 3 letter code willy nilly.
Good on the FAA controllers who actually got someone to eventually listen to reason. Let's just hope that the industry learns something from this and puts a stop to this potentially dangerous practice as of now.
It's no use all the safety authorities banging on about communication error being one of the most common causes of incidents, when those same authorities just bury their heads in the sand and say yes sir no sir when an airline "customer" comes up with yet another whimsical callsign change.