The elves are just arrogant. I mean look at the nightborne, the night elves were super arrogant efore the sundering, and that knocked some humility into them.. clearly not enough though when you consider the likes of MAiev and others, and the high elves' humility was short lived to once they started establishing t heir realm.
Now the human origin is known, and we have had quite a number of very outstanding humans that have had no trouble going toe to toe with any elf, it is clear that some elves (Looking at Shandris, Thalyssra, Alleria, Malfurion, Vereesa, Sylvanas and most of the SC think differently.
Some elves are okay