I am definitely one of those guys unfortunately. With proper bullets and shot placement, as well as with proper archery equipment, I have not see anything from an elk that lead me to believe they were super animals. HOWEVER, with poor shot placement, from a rifle or bow, they do have exceptional endurance and strength and will not just give up and wait for you to come shoot them again, like some different ungulates may do.
My small group of hunting partners are well over 40 elk between us. Have not had a single issue with a genuinely well placed arrow, or proper bullet. Or anything leading me to believe their vitals are any tougher than any other animal I've killed. Any and all issues with elk shots have been from poor shot placement.