I've met overly arrogant taru, well-mannered elvaan, taru who insist on playing melee jobs, and so on.
What's going on here is your mind is subject to hindsight bias. You don't remember the good people because you're making connections to the bad. You say when you see an elvaan, "yeah I bet he's a jerk". When that same elvaan fails to meet your negative expectations, you forget about him altogether later on.
I won't deny that there are some correlations there, but your bias is still the primary perpetrator here. Elvaan as a race DOES seem to draw the arrogant idiot sort, probably because of how Elvaan carry themselves. Galkas DO tend to believe they play a mage job very well because, let's face it, if they make it to AF they obviously aren't doing a horrible job despite low MP. Taru DO make good mages. Humes on a literal level do excel equally at every job. The thing is, you're only remembering the people who say all this, and are ignoring the VAST MAJORITY of mild-mannered players who are nice.