The main purpose of AI combat schemes is the non-unified combat AI. Bind to NPC classes is a bad idea since two NPC with the same class can have absolutely different spells, skills and equipment - we should take it in account at least.that won't be an option with unified AI anyways
But in this case we have to calculate scheme every time, or calculate it only when NPC stats are changed and just store it in NPC AI settings in ESM/ESP (post 1.0 feature).
And I do not see too much gain from hardcoding just 2-3 default schemes without ability to customize/select it.