Kamar-Taj's sorcerers were, by the standards of certain tabletop games on the market today, actually closer to "warlocks" or "occultists." They cast magic by making contracts with powerful beings.
Spells and gestures merely helped them focus on the process of "borrowing power" and shape that power into various forms.
Ordinary sorcerers had to spend years, or even decades, believing in the Vishanti before learning to wield their power. Therefore, if Harry wanted to use the Vishanti's power, he too had to believe in them.
Besides belief, using this kind of magic also required an Artifact: a "Sling Ring."
The Sling Ring strengthened a sorcerer's connection to deities beyond the dimensions. Harry did not know exactly where it came from, but he could not get one either.
All things considered, casting spells using Kamar-Taj's textbooks would be rather troublesome. Besides, Harry did not want to believe in the Vishanti.
The Vishanti could reclaim their power. Who knew when these big shots might take it back? There had been precedents in the comics.
Besides, Harry had his own supernatural abilities.
According to the system, Psychic Energy was an idealistic power with exceptional plasticity. Because of this trait, "everyone" loved Psychic Energy.
If he replaced the energy provided by the Vishanti with Psychic Energy, could he reproduce those spells?
With that thought, Harry closed his eyes. Complex runes began taking shape in his mind, while his hands slowly traced a circle through the air in accordance with his thoughts...
Sizzle—
A burst of purple sparks suddenly flashed in the air. Aside from the color, they looked exactly like the sparks Ancient One produced when casting spells!
But just like when Doctor Strange first used a portal, the sparks merely flickered in the air before falling silent...
The spell had failed, but Harry was