I respect what you're saying. And in addition, based on my experience, I respectfully suggest there is more to the picture.
First, I realize I was unclear: it's touching the edge that I was talking about, right as it's coming off the belt. You're absolutely right that if the mass of the blade is hot, the temper has already been messed up -- and the operator is a hack.
Hi,
Well , I also respect what you're saying, there is always more to the picture, its just a matter of
degrees 
How many mm deep does the damage go?
How bad was the damage?
Its kinda like bread , how big is the slice? And what color was it: light toast v. dark toast v. charcoal ?
The apex of the edge is like a 1 micron thick wire ,
it takes very little energy (fraction of 1 joule) to overheat to 2000F.
It can heat up real fast, as in milliseconds (1 second = 1000 milliseconds), and it cools off just as fast.
The video with the blowtorch is like a 5000 times magnification.
Mid-range or better blades usually "bite" properly on contact with hand stones (usually diamond for me) and that indicates that the steel at the edge is effectively the same as the steel in the mass of the blade.
Not sure exactly what you mean .... but isn't that type of check very coarse ? only detects heavy damage?
Only a belt sander or wet wheel can peel through it with any reasonable efficiency, after which the steel handles normally (for better or worse).
How many mm of blade width are you talking about?
Cutting into a coarse stone (~200grit) like you're trying to cut it in half removes metal rather quickly.
I'm not sure that all factory blades are messed up. That hasn't been my experience anyway.
I said "most" and that is only like half of "all" :P Is that statement hype or dry toast?
Dry grinding of all kinds seems "most" common
and thats bad
https://waikato.researchgateway.ac.nz/handle/10289/10004http://knifegrinders.com.au/SET/Edge_retention_worsening_by_felt_wheel.pdf
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