What I see missing is the right light. It appears you use DIY spot lights and flexible strip lights that are low in K value and lacking red and blue.. Fish and plants look washed out under 6000K, but vivid in high K and rich in red and blue spectrum. Also, you have to find a way to hide the cluster of overhead light fixtures.
Here is a pic of my 125 g set up similar to yours, and I do 75% WC weekly. I do not use substrate plants, but all Java ferns (broad leaf and narrow leaf Trident) attached to rock. I don’t think you necessarily need colored stem plants as all green is fine, allowing fish to bring out the color. All you need is more lush growth that takes time to establish. Don’t add frogbit as they will shade the plants below from getting lush.
Scattering the pebbles in the sea of sand is unnatural. It will look better if you can place them contiguous with the drift wood as an island
The big difference between yours and mine is lighting. In addition to strip LEDs sit on the glass top, I tied submersible LEDs inside the tank rims to optimize the footprint for light coverage.