You could argue all the building blocks are forms of curve fits, but that isn't a terribly useful statement even if true. If you can fit a curve to the desired behavior of any function, or composition of functions (which is a function) then you can solve any problem you can express the desired behavior of. Including the expressing of desired behavior for some other class if problems. Saying it is just curve fitting is like saying something is just math. The entirety of reality is just math.