Each one of those Solar Spheres was a powerful magic spell that had been temporarily sealed. The power of dozens of Solar Spheres exploding at the same time would never be as simple as one plus one equaling two.
In the previous battle, Lin Li used that exact move to almost defeat the ancient wyrm, but unfortunately, his efforts went up in smoke because of a slight error in control. It was actually not very difficult to seal just one Solar Sphere, and the difficulty lay in making all of them explode at the same time while allowing them to complement each other instead of canceling each other out.