One can equally suggest that you should provide evidence for your assertions. Who has hastily overhyped him? And going by any of the statistics collating sites, he is currently ranked in the top 5 on most of them.
So if he is blowing hot and cold, he is doing so at a better rate than anyone in the league other than Saka and Haaland. So more likely than not, it is you who's grossly underestimating him. He has been the best signing in the league so far this season... Bar none. Its not just City fans saying that. The statistics and performance metrics back it up.
You are making the same error many make, you think a player making mistakes means his overall performance is hot or cold. Wrong. He, just like Haaland, has flaws. But he also has a unique set of skills that severely tilts the balance in his team's favor. The difference when he is on and off the field is like night and day. It's why the metrics favor him and favor City. Even if he makes mistakes and makes the wrong decision ever so often.
Frankly, there is a worry that a lot of his teammates are beginning to expect too much from him as many stop moving and become fans when he gets on the ball.
The Stats don't lie.