There was one more advantage of having a Unique Skill.
The users of the Unique Skills could tweak their Unique Skill execution through the use of the Mesh.
It meant that the users of the Unique Skills had all the convenience of using the Mesh while enjoying the versatility of spell execution. Best of both worlds– so to speak.
Usually, the levels of Skills people could buy and use through the Mesh were matched according to their individualities. The users of the Mesh didn't have to do much while casting their Skills as a result. They only needed to pour mana into the Mesh and let it cast Skill almost automatically.
It means an A-Ranked Grandmaster would have all their Skills set as A-Ranked level by default unless they wanted to use a lesser form of that particular set of Skills. It also meant that Grandmasters didn't have access to S-Ranked Skills no matter how much they were willing to pay in terms of Menaka's Runes.