Deeply frustrating in the USA where one controller is managing multiple frequencies, but they’re not band-boxed together. You’re constantly talking over other people and vice-versa but you don’t even know you’re doing it. It’s slightly better with CPDLC but ultimately US air traffic control is some of the worst in the world.
Add to this the utter refusal of most American pilots to use standard phraseology because it doesn’t sound cool, and it’s simply a case of when, not if.