Does anyone know what the default perks are that the enemy takes?
You're making a massive assumption here, that Bethesda has created a consistent, rule-based system shared by all creatures, players, and npcs.
Hahahahaha, sorry, that was too funny. Bethesda would NEVER do something so...so...competent.
In reality, NPCs have waaayyyy larger health pools than the player, and in general deal waaaaay less damage. You can't really talk about what 'perks' they take - they're playing by different rules altogether.