Wouldn't you just want to sample a normalized curve and apply that? What is the use case where you want to use this iterative call, care about frame accuracy, but can't afford curve data?
With the explicit curve you have more control in the exact damping, too.
Exponential decay has the special property that it can be calculated from the current state with no additional data needed. With other kinds of interpolation curves, you need to additionally store the time the animation started.
Stated dabbling with game dev very recently so I'm curious about this!
Couldn't we get the delta, or for some animations use modulo arithmetic? Maybe mix in some gradient noise into the animation to make it seem organic to break the looping.
It would be illuminating if you showed an example of what you mean by using modulo arithmetic, or getting the delta; otherwise we can't comment on your idea.
With the explicit curve you have more control in the exact damping, too.