That is enough to make me never want to hire him to do anything for me, and to me that is pretty much the definition of unprofessional. You guys can defend him all you want, but that post was messed up, plain and simple. Maybe you missed the part that said "Fuck you, fuck all of you. With all the fucking might in the world, fuck you forever.", or maybe you're overlooking the entire rant because you happen to be bros with him. Well that shit is there, I'm looking at it right in front of me.
This is a business. He offers a service at a price, and bands and labels pay him their hard earned money for it. He is successful. I'm not sure why he feels entitled to so much more than that. He isn't doing them a favor and they don't "owe" him. He is not the only producer in town.