When the newly conjured blade cut through more than a finger's thickness in the sword, Toz stopped pushing it and separated the two weapons.
Although the old sword was a lot weaker than the newly created blade, that wasn't a reason to totally scrap it. Instead, Toz dissipated the blade's figure and poured the mana from the silvery blade into the matte grey sword, repairing the dent in the blade and enhancing the quality of the mana in it, giving the sword a slight radiance, despite the darkness mana coating it.
The reason that the blade had been so overwhelmingly superior to the sword was the difference in the quality of mana that made them. While the sword had a greater volume of mana packed into it, the sword still couldn't compare to the blade since the blade was made of mana, which was a lot purer, denser, and more efficient in its use.