I did the math on this wrong and in correcting my mistake I think I've found a possible parallel between Harry and the previous Starborn wizard. If the previous Starborn wizard was born 666 years before Harry was born I have to subtract 666 years from when Harry was born, not 666 years from the current date in the Dresdenverse. According to the official Dresden Files timeline Harry was born 26 years before the events in Storm Front. That's probably Oct. 31 1974 or 1975. So, that would mean the previous Starborn wizard was born in 1308 or 1309 A.D.
This is well before the Black Death hits Europe. It first enters Italy in 1347 and ravages Europe for about nine or ten years. So that Starborn wizard was around 38 or 39 years old at that time. This must be when Nicodemus made a major power move. Did Nicodemus spread the Black Death around 2/3 of the world simply to create despair, to bring on the apocalyptic mind state or did he believe he was "saving the world," as Dierdre put it, from an even greater Outsider threat? My guess is the earlier Starborn wizard was dealing with an Outsider threat at the same time. This person was able to defeat the Outsiders but not before Nicodemus got involved.
We know there is a disease; known only as Wormwood, which is being held by Mother Summer. Harry knows too, but right know he's facing a more immediate threat and will likely face others. Even if Harry defeats the last Titan that doesn't mean he's stopped the Outsiders. We can guess that Harry will one day have to face off against HWWB. I don't know if a direct one on one confrontation with Nemesis is possible. Maybe it can't be killed, who knows? But at some point Nicodemus will comeback and he will have a plan when he does so. Nic's plan will go way beyond getting revenge against Harry, Marcone or Mab, though that will probably be a part of it. I think Nicodemus is going to try to save the world from the Outsider threat by killing everyone on it, with Wormwood.
So the question is, "Will Harry be able to do better than the previous Starborn wizard, who defeated that Outsider threat, but at the cost of allowing Nicodemus to kill between 1/3 and 1/2 of the population of Europe?"