Olgar Shiverstone said:The real question is how do you make sure one Level 4 monster is the same as another ... and I don't know how they do that.
The answer is that we don't assume that all level 4 monsters are equal. That's where roles come in.
For instance, a level 1 party might not have much trouble against a pair of level 4 artillery monsters, if those monsters don't have any buddies around to protect them. The party runs forward, corners the monsters, and beats them down.
On the other hand, a level 1 party that fights a level 4 brute and a pair of level 2 artillery monsters might find that the artillery guys proved more troublesome. Sure, the brute was dealing more damage, but it took the fighter so long to beat him down that the artillery guys ventilated the group with volley after volley.
The roles are an admission that not all monsters are created equal, while providing a classification scheme that shows DMs *how* they are unequal.