In The Last Jedi- Rey isn’t the main character: Kylo Ren/Ben Solo is and Luke is a close second. Its that relationship and the fall out that fuels the plot.
I thought there was no fuel in this plot.
You may have a point that Ben Solo really is the protagonist. It felt like Rey was intended to be, but she hasn’t been a very engaging and relatable character. She’s likable enough, but her character development remains opaque. Maybe E9 will bring this full circle (like “Lost”) so her character makes sense.