I think people are often extra hard on Tiana due to her race

Nope.Her race has nothing to do with it.

Tiana has all the attributes that most people like, even without the racial bias. She's focused, driven, and hard-working, which most people see as role model material. Very few people recognize in her what I see: continual nitpicking and judgmental behavior towards others. Most people think nitpicking and judgment are both okay things to do.

The race thing is not what holds Tiana back. On sites I visited, parents were worried about the voodoo imagery with Facilier, and how to explain that type of magic to their kids. Other sites I visited, said that Randy Newman's songs on the soundtrack made things repetitive. But as I recall, James Cameron's Avatar came out that year in November, and it was a whole lot more exciting to watch than Tiana was.

I think she might be less loved if she were white, but she would still be more popular than the most hated princesses. Her work ethic is admirable regardless of her race.