Even taking into account the movement of spells from Transmutation to Conjuration, that doesn’t change the fact that Conjuration is still one of the most excellent schools a Wizard can have. And if Aarindarius was an Evoker(which is unlikely), then they would have found themselves to be somewhat lacking in performance compared to those who specialize in Conjuration. At the very least, they could have told V not to ban Conjuration, due to the versatility of the school! A mentor would want to prevent their students from making the mistakes they did, not repeat them.