I think this is overstated. In a starchy dish like pasta, I doubt 90% of people would notice a completely uncooked roux. And unless you're absolutely blasting

I think this is overstated. In a starchy dish like pasta, I doubt 90% of people would notice a completely uncooked roux. And unless you're absolutely blasting the heat, in which case most food behaves the same, there's no way for a roux to go from undercooked to burnt in a few seconds. It can take an hour to make a dark roux for gumbo.