He is certainly proving the haters wrong, but not because of them. He is simply doing his job, playing as good tennis as he can, peaking for the important events. Trying harder to win an ATP250 for the sake of proving someone wrong is not something I expect of him, that's not going to be his motivation, but he can certainly win it anyway.
Considering his first match of the year, he doesn't seem all that focused yet.
I can imagine from now on only Slams and Masters will be the real motivation factors.