The basic tenet of Jason Thompson's value is that he is currently a weak player, a borderline rotation figure, a player that will not help any team in the immediate future but has enough potential to become a very good role player down the road once he learns to play some defense and hopefully improves his scoring efficiency.
In other words, he is a player for tomorrow. Not today. If you give up a rotation worthy player for him, your team will get weaker this season ... but you'll gain a quality prospect for the future.
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As for Carl Landry, you acquire Landry for a scoring threat off the bench as an undersized PF. He is not a positive defensive player + he has become a major liability on the backboards (6/7 boards per 36 minutes -- very good rebounder when he first came into the league but has declined hugely since then). So you don't bring him in for defense/rebounding + his lack of size makes him a liability (defensively) against taller longer PFs. If your second unit needs some scoring punch, Landry can help you out.
Landry would be a useful backup PF for Oklahoma. I don't like how small OKC's frontcourt rotation would get with J.Green starting at the four and Ibaka shifting over to the backup five though. That puts a lot of pressure on whoever would be starting at center (Krstic?).
That said, trading Jeff Green for Carl Landry would be (somewhat) interesting. Move Ibaka into the starting lineup as a four and let Landry become their sixth man and scoring threat off the bench. Keep Krstic, N.Collison and Aldrich as your center rotation.
Giving Ibaka more minutes as a starting four improves their defense + rebounding + their ability to matchup against bigger front-lines defensively. Landry is a more reliable shot-creator and scorer than Jeff Green. Something OKC needs. A third scoring option behind Durant and Westbrook.
Carl Landry does not have as much range or versatility in his offensive repertoire as Jeff Green though. So, OKC's starting lineup would have some problems spacing the floor with Thabo, Ibaka/Landry and a starting C + Westbrook's limited jump shooting. Neither Ibaka or Landry could hide that. Green is quite useful here.
But it's an interesting idea ... some pluses, some minuses.
I'd probably make a J.Green for C.Landry trade ... although I'd look for a better offer elsewhere first. Jeff Green would likely have better trade value than that around the league. His reputation has always been bigger than his game.