There's no problem with that, but – do you often develop a Necromancer hero when playing as Fortress? I don't always do that....
Listen, I'm not trying to nitpick. I'm just talking about such a possibility. I think that you personally wouldn't even engage in such "things" :), however, it is quite a viable option ;). During my gaming experience, I used a method that, in turn, helped me win against my opponent :).
It simply doesn't speak to an additional bonus of the Titan's Castle, but rather – that you shouldn't consider Necropolis to be strong solely because of its magic. That's basically all I wanted to say :)
Sincerely.