This is a simple method I came up with for evaluating the power of mobs. A mob's power level is (HP*DPS*√BPS) where HP is health combined with armor (so if a mob has 20 health but 80% armor, that's 100 HP), DPS is damage per second (if a mob has more than one attack, it's the attack with the highest DPS, 0 damage counts as 0.1) and √BPS is the square root of the mob's speed in blocks per second.
Example: Steve's Power Level[]
Steve has 20 health. He can punch around 4 times a second for 1 damage each, so that's 4 DPS. He can move at 5.6 blocks per second when he's sprinting, and the square root of that is around 2.37. With tis 189.3. So Steve's power level is 189.3 with no armor.