But Merlin cares more about the human order than single individuals. I can just see the dickwizard turning Taylor into a martyr, or Artoria v2, and we all know how well that went for her. I mean, he's a failure of a mentor for Artoria in many different ways, fundamentally. Leonardo is far more likely to actually help Taylor as a person, treating her as a student in a manner likely remniscent of Annette, her skills are helpful no matter what Taylor chooses to do afterward, and with Inherent Wisdom, she can teach Taylor basically anything past her natural strengths. We have to get it, especially if Taylor can get Pioneer of the Stars (EX), which is fatebreaking, a super useful in a world rife with precogs, especially precogs that can work around blank spots (Contessa), and Ziz, where diablos ex machinas are more than a meme. Pretty much no one has that skill, let alone at EX.
Plus, Merlin is a prankster that would fuck with or manipulate Taylor, and this is a Taylor fresh off from bullying right after being lockered. It's a doubleplusungood idea to put them together right now.