Well we allways knew Yoda was not a nice person. The Jedi are not a "force of good in the galaxy" especially Yoda. This gets brought up in Clone Wars too.
I would argue that in the prequel era Yoda was a good person who was not good at his job. He was clearly one of the greatest Jedi Knights, but as a master and teacher he relies on mysticism way too much, so his advice is not particularly good. He also repeatedly fails to see the problems that are brewing right in front of him. And he is not sympathetic to Anakin. Obi-Wan was ten times the mentor that Yoda was.
When he's training Luke on Dagobah, he seems to set Luke up to make as many mistakes as possible.
If he was really as wise as everyone said he was, he would have stepped down in favor of someone more suitable to lead.