I always pursued by demon commander, when i'm playing archer, he always choose me as the first target to hit. I don't even attack him, so yes, its very unfun to play for some easy to kill classes at this game with such mechanics.
I think all warrior tank classes and some mage classes must have more initial "threat" than others.
One of the things I have been wondering wrt threat / aggro is the persistence of threat, decay rate, and how much is shared between groups. For instance, many anecdotes about encountering a new group of enemies, and they run past melee to go after a DPS unit even if nobody has fired yet. You could potentially get this behavior if threat is persistent, but appears hidden because the units ignore when set to idle. When someone hits them or they see someone to end their idle state, they might go back to the last set of threat.
Animals in waves seem to result in a bunch of weird happenings. Sometimes they don't seem to generate any reaction from the enemies, who are just idle and meandering around, even if perhaps one is engaging the animal. But once the mob or animal detects a player, they seem to all beeline for one of the players. Why is that? It is because the animals rarely generate more threat than one of the players?
It also seems to me the enemies have the player locations before actually seeing them or detecting them. The trickle enemies are almost always rounding corners heading for the players after they spawn. Or if an animal actually has taken the enemies out of idle near the end of the wave, sometimes they seem to all run to attack the players and you end up having to fight all the enemies at once.
I don't know what specific tests were done by specific individuals, but probably to look at any class bias in threat you need to go with level 1s and look at initial encounters on the map and see which classes are preferred before any damage is dealt to enemies, any threat increasing or decreasing passives or powers are applied, etc. Testing cursed treasure rooms this way would be difficult though since most treasure rooms aren't before any enemy encounters, but what you could do is have one guy solo the first mobs and leave 2 different classes idle in reserve, and then have them open the treasure room and see who it goes after.