At Villa, he usually got the ball in the inside left position. His fullback would always make the overlapping run to create space, and he had a strong, mobile centre forward making runs and occupying the central defenders ahead of him. He would also often receive the ball in transition with space to run at a retreating opposition that had just turned over the ball upfield.
None of this routinely happens at City. He's either playing false-9 and receiving the ball back-to-goal (or halfheartedly making runs to try and get on the end of crosses or through-balls), or wide left and getting the ball on the touchline with a defender tight to him, inconsistent overlapping from his fullback, and a packed opposition defence with no centre forward to worry about.
Which is not to say that we still shouldn't expect more from him, because we absolutely should. His performance against the Rags, where he played with what looked like true confidence and comfort for one of the few times in his nascent City career, should be the minimum we get from him. I just think both tactically and mentally this was a bigger step up than probably he or anyone else anticipated and it's taking him a long time to really feel natural in this side.
I do think that a big-money striker addition to take the pressure off his price tag, plus the usual second-season increase in understanding and application of City's system that we often see, will help him kick on next year.