It’s too early to judge. Yes the C919s have had some embarrassments (like cabins filled with fog) but I bet they’ll work out the growing pains quickly and learn. New models often have issues - remember the 787 having issues with composites, batteries, etc?

Also, Brazil has agreed to provide consultation and technology sharing between Embraer and Comac. And Embraer is highly competent, with aircraft used in the western world widely, so they’ll help with a lot of the real world issues. This is happening now because of BRICS momentum and Lula (friendly with Xi due to some common ideology). But I think whatever China gains from this new partnership will remain even once it ends. Eventually they’ll make the engines and avionics natively too, it’s only a matter of time.

Meanwhile Boeing has almost no innovation due to a mix of financially focused management, union labor culture, and a brain drain over the last 25 years. They’re not going to increase their lead anytime soon, which means the gap can only reduce.