A mob that just stands there and lets you whack on it has a name in most MMO's: Target Dummy
Mob behavior in MMO's is something that hasn't been explored to it's fullest potential in over 20yrs. It's time to move beyond path walking, low health running, meat sacks in most MMO's.
Dynamic Mob behavior models need to be implemented on spawn. Not every mob needs to be a special snowflake...but random mobs should have attributes that make them different. Maybe some mobs run and get friends? Maybe some mobs are afraid of fire? Maybe some mobs are merchants and have extra gold? Maybe some mobs spawn with multiple attributes and are renowned enough to have a name (random boss)? The possibilities are endless...and have RARELY if ever been explored in an MMO.
Dare to be different.
I agree that mobs in most games are behaving like "Training dummies", we will try to do our best in making them more dynamic and less predictable.