Agreed. The musical numbers encapsulate that feeling of grandiose joy that the films of the 90s oozed with.
Disney, under CEO Michael Eisner, did say mere years ago that they were foregoing traditional 2D animation. But when Bob Iger took over as CEO, he hired John Lasseter, head of Pixar, as Chief Creative Officer at Disney. He looks over literally everything Disney-related and even has greenlight authority. Lasseter said audiences merely want good stories, regardless how they're presented. The Princess and the Frog was made thanks to his vision and dedication to Disney's history of traditional animation.
Lasseter also said some characters, like Louis and Ray, can only be made in 2D animation. In 3D animation, characters have to behave much more believable, whereas audiences accept some cartoon-like qualities from 2D characters. Ray and Louis simply ooze with these little actions and moments.