First thought I had at the thread title was to say Mickey was probably the best mentor in the series (although I think of him really as a mentor only because of Riku's Story in CoM, I suppose), but I see I was beat to it. Of course, there's always the plot hole--introduced by KH2, grrrr--of why he let Maleficent go on the rampage for ten years, but aside from that, he was the only "mentor" figure that actually got down to business and did some things. I don't mind Yensid as much as others. Still, I'm glad he did at least something in KH3.
Plus, unlike the others, Mickey admits when he's wrong or there's some acknowledgment of it onscreen. Like when he was telling SDG to go during the 1000 Heartless Battle, for example. I think the writers want Yensid to be seen as an "infallible" Wise Man figure, to the point having a scene of him recognizing his failure in regards to the Nobodies would never happen. With Eraqus, on the other hand, I think the player recognizing how he was a failure was the point from the moment that character's introduced.