Just to chime in - on the one paw, I'm not sure Caelum is all that overpowered. But on the other, I'm not sure that it's all that limited in the late game, given a well designed pretender. I suspect it's a top-5 nation if not top 3.
False Horror : Overrated, imo - Seraphs using lightning bolt and/or frozen heart are about as effective.
Wrathful Skies - in my first two Caelum games, I haven't used it a single time. Both games I've one of the top two nations, without _ever_ using WS, and both games are post turn-50 now. I even had my pretender killed fairly early in one by a blitch (a B of a glitch
) which he is still crippled from, and in that game, turn 70ish, I haven't even found any good sites - enchantresses are the only recruitable non-nation mages I have. ( Spectres, Lamia Queens, etc, compensate quite well and don't require any luck in finding sites. )
If I hadn't used my somewhat limited charm and tact to manage some diplomacy, I wouldn't be a prime challenger in either game, despite the "huge" benefit of Caelum, and the decent benefit of being a strong intermediate player.
So - given that the game is meant primarily for MP, if all nations are supposed to be 100% equal, Caelum might get tweaked down. Then again, stronger players might let ... newer players have the nations like Caelum, Pythium, Arco, Atlantis and R'lyeh; maybe the Jotuns too and Vanheim. This lets the fresh blood experiment with the mightier nations, and allows the old dogs to prove that nation doesn't count for all that much by crushing them with Ulm and T'ien C'hi.
Something that might be nice, though, would be a game setting tweak that could be used to give a bonus / hindrance to a particular player. Say I get a 10% penalty to research and upkeep, while Cohen gets 20% extra gold, gems and research. Something like that might make mixed games with newbies and pros more interesting.