Andar knew there may be more powerful Mental Talents for a Mage, but for him, Gray Will even with its drawbacks was perfect. However, not every Mage would think so because of the strain it placed on their physique.
Disregarding the difficulty needed to acquire this talent, even operating it was impossible for an Acolyte without the Half-Empyrean physique Rowan bestowed on Andar that was further strengthened by his Awakening, he would not be surprised if a talent like Gray Will could only be used by Rank 4 Mages and higher.
Nevertheless, this gave him quite an advantage as an Acolyte that could not be equaled. In the case of Talisman Crafting, he was especially talented in this area, as the advantages of Gray Will lend itself more towards the Micro and worked better in a controlled environment.