In Shi Buyi's eyes, Lu Xuan's current combat strength was equivalent to that of his master.
They weren't very different from each other. Although this was an unconventional type of magic, it was impossible for Lu Xuan to display his full strength in his current situation. Even if he had consumed the rest of his mid-tier spirit stones, there was no way he could deal an extraordinary amount of damage.
It was probably similar to Xuanyangzi's peak combat strength, if not even be stronger. However, it had a limit; the attack couldn't exceed the limit of the Divine Transformation Realm.
Another thing to consider was that whereas Xuanyangzi could always maintain his peak combat strength, this was the only time Lu Xuan could only unleash such strength. He needed to continue consuming spirit stones to reach that same level of strength.
Even so, this was shocking enough!