A deal
The act of casting Runes was a skill that came naturally to every Scribe. It was not easy, a mistroke can mean a completely different rune and slight changes ripple through the effect of the rune, causing the rune to have a lesser or more powerful effect, it can cause its duration to be shaky, or shorter.
According to the books that he had bought from the Gnosis society, Zane had learned more about inscribing runes, it was not about raw power but control and finesse. To cast a spell efficiently, you need to channel the right amount of mana. That was the reason that he practices the rune over and over again, until they are so familiar that they become instinctive.
Practicing the runes also came with an advantage. It takes longer to cast. By the time he reached the criteria for the clearance of the Inca Successor Dungeon, he only needed 3 seconds to cast the Word of Frost but for a very fast or more powerful energy; three seconds was all that they needed.