I'll give him a 4. He really stopped taking himself so seriously especially after coming clean about his hair plug situation that nearly ended his career. I think it was a good 'Oh Shit' moment that helped him realize how fortunate he is to be in the position he is in. Definitely loses points due to the nepotism thing (really common in broadcast media).
My favorite moment was from a live chat he did on Deadspin a few years ago. The link I found to the story no longer has any of the transcript available, which sucks.
https://deadspin.com/ask-joe-buck-whatever-your-despicable-heart-desires-5958950
He was mostly getting destroyed by people writing in and he took it all in stride. My favorite recollection was,
DS Chat Participant, "Every time you respond in this chat just makes me hate you more."
Joe Buck, "Awesome."
As far as the whole bias thing, it isn't there. Either he is neutral and unbiased, or he just hates every fan base with equal amounts of passion, which would also make him unbiased. I live out in the Chicago burbs, and at no point during their 2016 WS run did I ever think "Jesus, Joe really hates the Cubs." despite the insistence from family and friends out here that he did. During 2018 I asked my wife if she thought Joe was rooting against the Sox, and she said it didn't even cross her mind.
He was 2.5 pre-hairplug incident. 4.0 since he came clean about it.