These flights are too long period. Doesn’t matter if it’s in Y, J or F.
My max for a direct flight in J/F is 8 hours. Beyond that I try to break it up.
8 hours? Short haul! Try crossing the Pacific, you can do that from the US to Australia in two hops, but one of them is at least 10 hours. (I've flown no 5 [in PE] and 13 [in Y], both doable.)
That's why Americans feel like they're the center of the universe, except they couldn't even make it across the pacific.
Haven't done any of these but have flown one that's almost certainly in the 21-30 range of this list: YYZ to HKG. Absolute marathon of a flight.
I "get" to do #15 after a trip to MLE. First one this long. (that's what she said)
All my others have been short haul, 8 and 9 hours.
My wife & I just did #1 (SIN - JFK) in January. Great airline & great flight, 16.5 hours.