I spend quite a lot of time listening to the folks who promoted and voted for Trump. His voters vastly overestimated him, and he has a LONG track record of failing to live up to their fantasies, from the deep state that he didn't fix through wars that he didn't end through felony convictions that he didn't overcome.
So no, he wasn't elected because people underestimated him. How would that even work?
He was elected specifically because his voters overestimated him.