To be honest, I don't much care for unique tile improvements in general. As I said, in my post, to get a benefit from the terrace farm tile improvement which is better than what a normal farm on the hill provides, the terrace farm requires a minimum of 3 adjacent mountain tiles (so three unworkable tiles). That is kind of a hard trade off for some

and doesn't always occur. I find pasture resources and camp resources to be better examples of tiles which provide

and

(and sometimes

as well). The terrace farm is just not good enough to replace a UB or additional UU.
Is it thematic? Sure.
Does it have a measurable game effect? Yes.
Is it situational? Unfortunately yes.
Is it stronger than the other remaining civs on the list? Not at all!