The problem with Piety is that it's failing to perform its primary function. Peity's primary function is making
excess happiness more valuble. It does this through reducing the happiness bucket for GAs and giving you culture for excess happiness. Yet there's not enough policies in the tree that enchance this function, and there's also not enough reasons to keep excess happiness floating around - since those luxuries can be sold to the AI for 300 gold a pop.
There's really only one situation in which you have a ton of excess happiness and that's when you have a small empire with a ton of city-state allies that are gifting you resources that can't be resold to the AI for profit (and you probably got those allies by selling your resources to the AI in the first place).
But in that case, if you have a ton of city-state allies, you'll get more benefit out of Patronage than you would Piety, unless you are going for culture and are picking up both trees anyways.
I think something really needs to be done with Reformation - an additional ability that would make excess happiness more valuble. Perhaps a hammer boost? What about a flat +15% bonus to hammer production if your empire has 15+ excess happiness (like Rationalism's Soveignity, but with higher requirements) or a percentage increase based on the amount of excess happiness.
Or perhaps the happiness bucket should be adjusted down (though with a eye on how this will effect Persia), and Great People as well should be balanced more so that people don't just rely on spamming them for thier Golden Ages.
The primary problem with Peity is that excess happiness is not valuble enough and Peity does not make it much more valuble.
I do agree that MoH should be either 100% or at the very least 75% of excess happiness gets recouped as culture.
Due to poor combat AI, there's no effective way to balance Autocracy yet. It's just not worth getting this late in the game if you're warmongering.
Could you elaborate on that statement? Do you mean that you shouldn't reach the industrial era if you are warmongering or that it's just not worth it for the point that you get it? I think that Autocracy has one of the most powerful Policies in the game: Militarism (-33% purchase cost on units). Combined with Big Ben and Commerce you get a whopping -83% discount on purchased units that you can all rush-buy in a city with a military academy and possibly the Heroic Epic. You can even keep gifting these elite units to a city-state being besiged by a rival to clear the city-hex and rush-buy more in the city with the most military buildings.