"Nice" is a very subjective concept and can be used to describe people in both complimentary and derogatory ways. In my experience niceness and competence are in no way correlated – I have known nice people who were good at their jobs and assholes who were good at their jobs, as well as some of both who were terrible at their jobs. It is perfectly possible to be both competent and nice.

Given the choice between two persons of equal competence, where one is nice and one is not, I would be surprised if anybody chose the less nice one, all other things being equal.

I suggest continuing to be genuine, rather than focusing on "niceness", and not allowing a single comment on the internet to make you feel self-conscious about your character.