[Fantomen]

Fatigue applied to slaves from spells cast by the master don't "cap" at 200, any spill over fatigue does damage to the slaves. Reinvigoration works because it removes enough fatigue that the slaves usually don't reach 200 and start taking damage. But if they are at 199 they're gonna take quite some damage from a big spell.

What "other fatigue reducing spells" are you talking about? There is only earthpower and relief, none of which are viable for this.

But anyhow, in your example, if your "first master" casts a tiny spell each turn to stop slaves from casting. Then how is the slaves going to accidentally cast sabbath master? Because, you know, they wont cast **** either way. So in that example the change to sabbath spells makes 0 difference, except the very good difference that you don't have to micro slaves for the slaves/can place them where you want.