The 90 degree specification allows effective use of the spine with a ferro rod. I am sure people have come out of the woods alive carrying steel other than high carbon (like stainless).

The capabilities of the knife owner with respect to sharpening are probably more important than the type of grind.

It is possible to escape disaster with only a SAK or even a multi tool - they may be more versatile and useful than a fixed blade knife for many (not all) situations.