And wee one has it correct.
The wing isn't the prime issue.
Thrust, or lack thereof, is the real problem.
Aircraft are genuinely falling out of the flight levels. There is an amazing use of the old boy network, sheer luck and commercial cowardice working to ensure you aren't reading about this in Aero or the crash comics.
Danny and I do not speak with forked tongue. Ain't enough thrust at max alt to keep you out of trouble. Happened to me in a light, 27k aircraft over Hungary - it can happen to you.
I file no level ever above 380 for every trip regardless of weight as SOP
Regards
Rob