What I don't understand is why there isn't a general rendering priority order in place...

The order should ALWAYS be:

Yourself
Enemies
Your party/alliance
Your party's/alliance's pets
Other players
Other players' pets
Minions

This priority order should be used for rendering characters at all times everywhere in the game. If they did this there would be no issues. I don't know why this isn't already in place considering how many other MMOs do this...