Marcone was a vanilla mortal before he picked up Namshiel. My understanding was that the amount of power someone could access was a matter of genetics. If Marcone had the kind of inborn talent that Harry had, it should have manifested on its own, before Namshiel. Marcone would have been summoning monsters, ripping holes in reality, or doing other mad sorcerer stuff on accident his entire life.
I think the easiest excuse is that Namshiel somehow "gave" Marcone a big magical talent, but there's a problem with that. All of the fallen angels are ancient and know basically everything there is to know—presumably also about magic. So then, all of the Knights of the Blackened Denarius should be slinging mad spells like pros, especially the smarter carriers. Instead, you've got guys like snake boy the one-hit wonder and Tessa's mob of oddly transformed goons.
So... what gives? Any ideas?