If I remember correctly, Frozen was the first "Disney Renaissance-esque" (musical, grand plot) movie since, well, the Disney renaissance. I think that line in the Frozen trailer had less to do with "The Lion King is the best Disney movie ever and we are comparing ours to it" and far more "look how we are finally returning to form".
Similarly, it's kinda funny reading about Zootopia's marketing since we know how well it did after release. But prior to release, it had all of the warning signs that Disney wasn't all that comfortable with it: March release date (when their less popular movies come out), the first trailer (https://youtu.be/5nP9hU8eUfE) was... terrible. The seconds trailer, while I personally like, I get the impression others were not so impressed by. But nevertheless, in that second trailer (https://youtu.be/jWM0ct-OLsM), you also see Disney pushing the whole "brought to you by the same creators that made Frozen, Wreck-it Ralph..." (and a few other movies I forgot) even though the actual creative team of Zootopia almost had nothing to do with those movies, just the backing financing studio. But hey, those movies did well, and we have no confidence about this one, but those movies you liked, so come and see our new one!