If your primary focus is thrash metal rhythm, I can see why the MegaDrive wasn't for you. It really shines as a lead player's pickup, as you said. I was mainly responding to your use of the D-Activator and D-Sonic models previously. I found both to be a bit sterile, as well, though the D-Activator was the better of the two, in my opinion. The Super D is more lively, but doesn't really have the clarity for thrash metal rhythms. That's why I figured you should try the Illuminator...it's not like most of the other DiMarzios you've tried. It's punchy, balanced, cuts well and is plenty articulate, but still has great expressiveness and awesome crunch down low. Not too sterile, very versatile, even compared to the Crunch Lab that preceded it.
Any reason why you're not considering another Duncan, though? Just looking for something a little different?