In terms of defense, the Suns have it already, but even an old Howard could not stop Giannis as he really can dominate inside. Suns have to play as a team as the Warriors did, they have Booker and CP3 as their superstars but their level of consistency dropped last season.
When he went to the Lakers with their run on the bubble, Howard wasn't a problem in and out of the court for the Lakers. Sure he still have that antics, nevertheless he has proven himself to be effective playing the center with Anthony Davis.
Same when he moved to Sixers, no issues whatsoever with him and Joel Embiid. So not sure what you mean by attitude because it seems that he has matured already and knows where to have that "good attitude" inserted. And he didn't destroy the good chemistry in Sixers, it's that he was not a perfect fit, that's the way I look at it and that's why they have given him up and Lakers pick him up again to play last season. But right now, no teams are interested on his service.