I remember the same comments.
Its just that everytime I ask where the facts came from there is no answer.
It seems like an Urban legend, or more accurately, a Boatbuilders legend.

As far as I know there is a limited number of hardener chemicals to choose from.
Since the formulas are treated as "business secrets" most of us will never know exactly what's in the major epoxy's and the 50 copy cats.

That said, I agree with the caution to take precautions.
I just don't know of any facts that say you should single out one of the suppliers.

If it was just a fact of being "more concentrated" it should be easy to "dilute" the components and get around the fingerpointing.
But if it is a different chemical composition, the ratio may just be a consequence of how each individual hardener works.

No I'm not out to sell or defend any specific brand.
Yes, I do use West.

I get a lot of reaction to Cedar dust, and nothing from Epoxy.

I'll quit asking this question each time this comes up, whenever a recognizable expert tells us what is the active, and hazardous component in the Hardener. That assumes there is some way to tell which hardener is actually more dangerous by itself.

Since sensitivity does not uniformly happen, I doubt even a ranking of hazards is possible between the various Epoxy brands.