Nope, that's still the wrong way round. If "usefulness" is Y and "knowledge" is X, and you needs lots of knowledge before it's useful, then the curve is shallow.
Having thought this through a little more, it seems more like bumps. For example, you can't do anything with Vim until you learn basic motion and insertion. That a bump. Then, you learn how to use the more complex motions, and get another bump. With something that has a steep learning curve it is done in bumps, rather than being smooth, because partial knowledge doesn't help any. If you think about it, if you only know the j and r commands in vim, you're not going to be doing anything at all, you're going to need to know at least hjkli before you can even use it.