here's another wya to look at it as well, from SA and Dallas' perspective.
SA:
Does anyone think SA worries about Shawn Marion on offense or Defense? He's been a non-factor against them since he's come into the league. So basically, they look at a situation where they look at us and know Shawn Marion doesn't do anything to them defensively and when he's on the court on offense, we basically play 4 on 5. HOWEVER, with Lewis, we give them a match-up nightmare on offense, thus, a plus for us.
For Dallas - THEY MUST HATE THIS DEAL and here's why:
Dirk AND Josh Howard had their way with Marion on offense and again, this year, Shawn did next to nothing on offense. So again, you might have Dirk use Lewis, but again, backing down and shooting over a 6'11 guy is thougher than a 6'7 guy and Howard with a 4 inch difference won't be able to back Lewis down the way he did. Will he get beat off the dirbble by those guys? Yeah, but Marion did as well, thus it's a wash on defense.
HOWEVER, because Marion did nothing on offense, Howard or Nowitzki could save energy for offense, whereas Lewis can back down Howard and take Nowitzki off the dribble.
Thus, against both teams, it's a relative wash on defense considering Marion's had no impact versus those clubs defensively but Lewis creates match-up NIGHTMARES for them on defense.
And this doens't even mention the fact that we get a lotto pick where we might pick up a shotblocker.
I guarantee you Avery and Pop don't wnat this deal to go down. They both attack Marion at every chance and both know how to make him next to useless on offense. That won't happen with Lewis, not to mention getting another stud in here.