I don’t think we are in disagreement about fault on both sides. This could have been avoided at many points along the way - I would include Vistajet Operations, both pilots, and all the ATC units. Any of them could have averted this situation. I maintain that it’s stupid to use colloquial phrases that are not clear to foreign registered aircraft with foreign pilots in it. If the language had been clear the pilot would not have said “affirm” as max land is 78,000lbs and they would have been 99,000 and they were going to Athens. Equally, the pilots should have checked that the tower were clear on what they were trying to do. And in the air they should have understood more clearly the airspace and environment they were working in.
America is one of the easiest countries to fly in. Your ATC is generally very switched on, your airspace structure is much clearer than most other countries I have flown in, and if you ask how to do things everyone is very helpful. But it could be better and working out what went wrong here will help. It’s not dissimilar to the shambles that went on with the EVA down in LA. Standard ATC works. Non standard might work. But it might not.