Ahriman
Tyrant
I've already agreed that Aesthetics seems quite powerful. But in response to your concern: if it's that strong, wouldn't everyone use it? And if they don't, wouldn't that be a good test of whether or not it's OP?
It might be a good test of that, but it wouldn't really be a good test of anything else. Having lots of free military units, food and culture will tend to severely distort the value of other strategies. For example, if you're getting lots of food free, then your emphasis should be on happiness policies and buildings, and specialists will be super-powerful. Military production bonuses (eg from Honor or blast furnace) will be less valuable if you're getting lots of free military units. Era-beelining will be very strong (to get Aesthetics asap, and to get into higher-era CS benefits). Strategies that involve conquering CSs will be very weak. And so forth.