I wouldn't say that Joe Johnson sucks with Atlanta, he's been great with Atlanta he's currently fifth in the league in scoring, and he's a very good passer, and he plays decent defense, he can jack up the three as well, will give you around five rebounds as well.
I believe that Ron Artest is an underrated player because of is past, and the suspensions he's got from the NBA. If he didn't have a bad rep he'd be known has a great player in this league.
The reason why he was 10 times better is because they had a player named Steve Nash, he gave him the ball basically anytime he was open, but I wouldn't say that Johnson was playing better in Phoenix because he's considered as a superstar now, but when he was in Phoenix he was considered as a good player.
I would agree with you that a lot of basketball fans think Steve Nash isn't all that good, and I don't know why they say that, because like you mentioned he makes the players better then their really are. Just take Diaw for example, he had potential while playing with the Hawks but didn't do anything, and he starts playing with the Suns and now he's considered as a star in this league. But I believe only basketball fans think that Nash ain't all that good, but people who actually knows that there talking think he's a superstar in this league. People who actually played this game.