It is a bold statement! Since the 80s, the princess movies have had an element or two that you could consider progressive, but since John Lasseter has taken over things have progressed by leaps and bounds.

Princess and the Frog
Tiana is the only princess to promote the idea of working instead of wishing. Her prince is an oaf though. Also, being honest, I feel uncomfortable in homogeneous groups, so, while I feel like I'm being an insipid Social Justice Warrior or maybe some weird kind of over-PC racist for saying so, I'm just really glad she's black... I can't believe it took until 2009.

Tangled
Rapunzel is the first not-so-graceful princess, and the first to have a male lead on equal footing with her. I would argue that Tangled meets 6 of Frozen's 7 progressive points on at least some level.

Brave
Pixar makes a princess movie, and it's the first one that doesn't revolve around romantic love being the end-all-be-all for a girl.

Frozen
Possibly empowered by the success of each of the previous moves, Lasseter produces a "princess" movie with two strong female leads, that has romantic love as just a side plot, and tosses in a two-father family for good measure. I hope to see this as the new standard of movies marketed to girls.