I don't think either FAST or RATAN are capable of radar astronomy (i.e. sending out a strong radio pulse and listening to the reflection). Arecibo's radar capability has led to numerous important discoveries, taught us a great deal about Mercury (including the period of its rotation and the fact that it has ice at its poles), and is still one of the most effective tools we have for examining low albedo solid objects within a few AU of earth (e.g. asteroids).

Even without that, Arecibo is still a very capable observatory, and it's not like we have an excess capacity of observatories doing this sort of work. We could have twice as many similar facilities and still keep them all busy.

Speaking of which FAST also illustrates that such dishes are constructed with material/structure that cannot take heavy loads. FAST requires maintenance personnel on the dish surface to be attached to helium balloons so that their weight is reduced during inspection/maintanence related walking on the dish.