I'm quite alright with that
This rather will never change in C2... But I must say I like this kind of system, working per frame not per sheet. It makes placing image points really quick. You can make all your frames at certain size, import them, put your image point when you want and "apply to whole animation" and crop your frames.
It's not that easy when you importing entire sprite sheet and have to manually "cut out" every part of the texture to be used as a frame.
But with custom sprite sheets you can pack more images on one texture...
Both methods have their pros and cons...
That's the part i hate the most in UE4. You can press a button and all images will be automatically cut out... but then they all will have different sizes and placing image points on them after that is incredibly painful... Almost as using Image editor in C2 to copy/paste animations and animation frames xD