Yeah, I agree. Still, I guess you could look at it depending on his regeneration. As we've seen, The Master went from "diabolical" to "driven by revenge" to "downright insane". So, it's possible this earlier life could have been less "evil", in its own right. Of course, if he'd been trapped on Earth for a few hundred years, it might be alot of why he hates The Doctor.

But, that's all speculation. It might be just better to use the Monk as a completely seperate foe. A little diversity, and all that...