It's not that some testing is performed.
The issue / concern, is the testing that isn't performed, or the degree of actual testing, because grandfathering rules are invoked.
If you can start with the 772, and invoke pre-existing 747 and 707 certification for partial grandfathering, then take 772 certification and use grandfathering to take weights from 545K to 766K, are there risks?
Proponents will argue look how safe the 777 has been. Grandfathering works. The cynic in me says, with every layer of grandfathering does the 'luck' factor increase? When is it time to start with a clean sheet? Would the 777X be a safer and better aircraft if it was a clean sheet?
Do you know which grandfathering rules are being invoked? Do you know what is and isn’t being tested? Do you really think that the 772 relied on grandfathering from the 707 and 747?
If the fuselage and wings are being tested like a new design, the entire flight envelope is tested and all new systems and software are tested, what is being left out?
So to clarify, you are confirming Boeing hasn't requested / isn't negotiating any grandfathering for the 779 vis a vis earlier 777 models and 787? Boeing and the FAA are treating the 779 as a 'clean sheet'.
They did. https://www.wsj.com/articles/boeing-777x-clears-hurdle-with-faa-1398916634
(I see a lot of diverision, dismissing, probably by members that had to reboot last week when their sources of truth where changing their minds and even corrected, top down. Lets stay on topic. )
I think using the the 77W as certification base for the for 777-9, and the using the 777-200 as certification base for the 77W means you are creating an new aircraft not using the latest certification standards. That saves times and money. That is why Boeing does it in the first place.
The discussion is if we should allow corporations to certify new aircraft (new wings, tails, cockpit, engines, systems, landing gear, dimensions, fuselage, materials) using old certification standard using older, different aircraft as reference.
Apparently authorities are changing their minds too and will work to curtail grandfathering certification data, requirements and using really far fetched certification bases. So we seem to be moving in the right direction on by-passing new certification standards.
The rules are set, and then the OEM's operate tactically within them.
FAA and EASA officials have already been meeting in neutral locations on the QT since January 2019, with phased removal / deletion of grandfathering top of the agenda.
Over the years, the FAA / EASA have implemented new and tougher design requirements, but a derivative gets many of the designs grandfathered in. I think the 777X is an extreme example of a new aircraft benefiting from a barely acceptable grandfathering process. I think independent people should ask the FAA where they draw the line, and what factors in for them.