well, look - technically this thread is about Zen's conceptual balance mod
now, the mod does not address flying, whether or not flying is overpowered. But the caelum problem resides in a combination of synergistic effects: flying + false horrors + wrath, for the most part (exceptionally cheap mages, able to easily get by w/ the watchtowers and sloth-3, also). Zen's mod at least cuts out false horror spam and makes wrathful skies more difficult to cast. both of these, in and of themselves, help balance out the problems. (the scale mod should also end up making caelum pay a bit more for taking sloth -3 as well).