Kintara
Warlord
I don't understand why you would think so. If you don't have mountains, and no mountains starts seem common from what I've seen, then they're little better than wet hills. The main bonus, in my opinion, of terrace farms, are actually the early benefit of working those hybrid tiles, assuming you get some good ones. But it's a mixed blessing, not pure long term gold, due to the danger of being topped out later on.Not to even mention the crazy defensive bonuses. Both the Inca and Aztec have food-based Uniques, which themselves are based on exploiting unreliable terrain. I just find the somewhat-more-reliable Terrace Farm to be better in the long run than the less reliable, but more exploitable-in-a-perfect-roll Floating Garden.
There is really no way, in my opinion, that the Floating Gardens are less reliable. They apply their bonus to every single food point you generate in the city. The lakes bonus isn't about exploiting unreliable terrain at all. The lakes aspect, in fact, helps you build water mills in more cities than you otherwise might be able to.