I get it from a commercial point of view that they have to implement a plethora of different kinds of Aliens, but it really cheapens the creature and makes the game feel unnecessarily arcade-like.
If I was in charge of this I would make the Runner, Burster, Spitter and Prowler use the same model as the Runner and have them all be named Runner. In this way the Runner cannon fodder unit will keep the player on her/his toes as one doesn't know how the randomly spawned Runner will behave and attack and how hard or easy it will be to kill.
It would make the game more interesting and less predictable as the players will have to be more cautious with each and every Runner they face as they don't know if it will explosively spray the area with acid blood when it dies, or if it's a pouncing ammo sink, or if prefers to spit acid at you from afar, or if it's just another tail-swiping zombie on speed.