The biggest drawback with the Dike – well, along with it coming late, and the hammer cost – is that the benefit isn’t really all that great, when it comes to generic water tiles. 2F 1H 1C is a pre-Biology riverside plains farm, something nobody wants to work many of. The same criticism could be levelled at Moai, except that because there’s only one Moai, you can choose to build it in the rare spot where you can get the extra hammer on multiple seafood or lake tiles, which are worth working.
One thing I do like about the Dike is that you don’t need to be riverside to build it, but can still reap the benefit on river tiles. That’s handy when you’ve captured a coastal AI city that is 1 tile off the river, but would otherwise benefit from a Levee.
I like the Terrace, particularly on Epic/Marathon, where even a whipped/chopped Monument means 15 or 30 turns to the border pop. Cutting that time in half feels like a huge boost. And for a lark, I once played an unrestricted leader game as Pacal of the Inca. Emperor felt like Noble.