I see your point.
To me the 520 conversion isn't an upward modification.
It's more like a reduction.
My Supersprox sprocket is the tri-metal one with the steel teeth.
My chain is rated at 10,400, I just checked, it's not 10,500.
And I'm not known for my chain maintenance.
I just ride, lube, wipe, repeat.
My last chain I put about 11,000 (hard) miles on & never cleaned it once.
This chain I will try to take more care of, but I doubt it will happen.
If it handles my abuse better that the last final drive I had, I'll be happy.