I spoke to Revolutionary Jack on Twitter, and he brought up a good point: It makes sense (to an extent) to use a villain like this because it will make the split-up more foegettable and easier for a new writer to start his run without baggage. Like how MJ's kidnapper in the Mackie era was a nobody and JMS was able to ignore him, while OMD is harder to ignore because Mephisto is a known Marvel villain.
I mean, that's at least one upside to using a villain no one remembers or cares about to solve the mystery.