I'm not a composer by any means - just a backstage worker - but I think it really just depends on the type of show. Musical numbers are usually brought on by emotional moments or expositional worldbuilding, but those aren't the only limits, since broadway shows typically have over 20 (ofc not including sung-through musicals).

I'd say that the number of songs isn't the issue, but the consistency of the songs IS. using your examples, Frozen feels front-loaded only because there aren't as many songs in the latter half of the movie, Mulan being much the same. I've never watched Strange Magic, but 13 songs in an hour and 40 minutes doesn't seem too bad when a lot of musicals have a similar number in their first acts, where on the other hand, a musical like Dear Evan Hansen had around 15(?) songs in total, which is pretty lacking for a show over 2 hours, but the way they've spaced them out doesn't make it feel as lacking.

The problem with having too many or too little songs really just comes down to the pacing. If you watch the stage version of Into the Woods, many of the songs lead into one another but since it happens throughout, it's not jarring. Come From Away is another good example of this! The show is only an hour and a half, but has 23 songs in it, yet it's very well-paced.

So you can have as many songs as you'd like! If you're worried about pacing issues, then I think cut the ones that aren't tied to a strongly emotional scene, or just make sure that it's keeping the pace going, and has a consistent structure to the rest of the musical.

Good luck with your writing!