A painful exploration of what it's like when you don't know what you're trying to say, The Greatest Showman well deserves its 55% rating on Rotten Tomatoes.
If you want to break that 90% mark, you need a story. You need a Main Character Throughline that brings the Audience into the story. You need a challenging Influence Character perspective to shake up the Main Character's justifications. And you need some kind of Relationship Throughline between the two to compliment the conflict everyone experiences in the Overall Story Throughline.
The fact that Showman is a musical is no excuse. Moulin Rouge! is a musical and shines as a brilliant example of what happens when you combine song and dance with a meaningful and complete narrative.
If you like music videos, you'll love The Greatest Showman. If you like meaningful entertainment, it's best to set the filter for 90% and above.