: His being, soul and pressence were more powerful.
A couple of comments.
One, Myrdred is an avatara hero. So? Being a "hero" just means he's a unique and somewhat stronger being compared to the standard unit. Not that he's the greatest avatara, although a case for that on basis of Dream power could be made.
Two, Connacht is the Saivor. Presumably, Mazz would know that if anyone, so he'd need/deserve this knowledge to use properly so he can save the world.
And of course, Three...
Myrdred is simply not someone I'd trust if I was Mazzarin.
I'd established the avatara to stand for the Light. Not to merely seek power at any and all costs. In fact, I actively stood against doing so. So Myrdred being associated with the Warlocks, instead of a sign of how strong he was, would be tantamount to treason to Mazzarin, I think.
Seraph