Many posters here find fault with Emirates. Emirates is Boeings biggest customer in regards to the 777 and now the biggest customer in regards to the 777-X.
IMO Boeing is not living up to promises.
The delivery delay is all on Boeing, or GE as it is.
If the 777-9 does not hit contractual specs in regards to the contracts with Emirates, be it the frame itself or the engines, Boeing must expect the contract being challenged by Emirates.
The other day Jim Clark complained about Boeing not affirming data in regards to the performance of the 777-9.
There have been enough test flights for Boeing to start getting real world numbers. If those numbers were good, they would be all over Emirates to tell them that they hit specs or beat specs. Boeing not doing that points to trouble.
If Emirates would cut the 777-9, that means loss of 115 orders. As the backlog of 777 is according to Boeing 266 frames only, with a few 777 mixed in, that would not leave many 777-9 on order and the question would become how viable the 777-9 is without the Emirates order.
Boeing must be relieved there are no A.Net posters on their payroll negotiating with their customers.
A milestone is approaching for 777X customers to re-affirm unconditional and conditional orders, AND qualify for Tier 2 and 3 compensation credits.
One tier covers late delivery, and the balance 'other'. Presumably EK are unwilling to accept the compensation formula until they have detailed deficit information, and a guaranteed timeframe for rectification.
As you state, given the multiple year delays, most customers would expect performance enhancement announcements to be trickling out by now, while the reverse seems to be the case.
The fact neither Boeing or EK are quoting actual performance, suggests the data doesn't exist, or Boeing isn't satisfied with the numbers, or................