Maybe the driving instructor wanted to impress upon you the importance of respecting the STOP sign with this story? Maybe it's true in some cases, but somehow I can't imagine that at an intersection with very bad visibility the traffic planners just say "let's start with only a Give Way sign and see how many accidents happen, if it's too bad we can always replace it with a STOP sign"?
It's true however that some countries are more prone to what I call "traffic restrictions overshoot" then others - e.g. in Italy there are many stretches of highway limited to 50 km/h, apparently in hopes that drivers will at least reduce their speed to 70-80 km/h, and many STOP signs hoping that drivers will at least slow down at the intersection.
But I'd think a Give Way sign should suffice in practice even if the intersection has poor visibility. Only if the intersection proves to cheat drivers in to thinking the visibility is not so bad (and hence drivers won't slow down enough) is a Stop sign needed?
It's true however that some countries are more prone to what I call "traffic restrictions overshoot" then others - e.g. in Italy there are many stretches of highway limited to 50 km/h, apparently in hopes that drivers will at least reduce their speed to 70-80 km/h, and many STOP signs hoping that drivers will at least slow down at the intersection.