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.

Engines are a tough cookie to crack since the material science need to do it with high performance and economy is a tightly guarded secret and difficult to reverse engineer. They’ve been dumping billions into this but it’s still a moat (they keep claiming that they have engines ready for high performance/high mileage to overhaul military use, but keep needing to use Russian ones instead).

Well, what doesn't make any sense to me is why COMAC let Bombardier sell Airbus the A220.

That jet has lots of sales, and half ownership with production rights would be fantastic for COMAC.

Canadian government would never allow a Chinese SOE to take over something like the Bombardier C series

Wait a second. Did Bombardier have other offers for the C Series? It's a great plane but the circumstances of the sale are unknown to me. It happened so fast.

As far as I know, they had no other choice. Boeing was rumored to be working with them for a while on an acquisition, but then abandoned them and left them in a very vulnerable position. Smaller companies without lots of working capital cannot absorb a big strategic change like that. They had probably already had discussions with Airbus that made closing it out much quicker than any alternative.

Don't draw conclusions too fast. Airbus breakthrough was when it sold its A300 to eastern airlines. If I remember correctly it was a no strings attached deal where they could give them back.