The more I think about this deal, the more it reminds me of the Perk deal for the C's.
You are the odds on favorite to come out of your conference to the finals, but trade away a key piece, based on longterm contract concerns, for a package that is a very stong haul...but still might make you a worse team for the championship run this year.
Of course, the difference is that this is being done much earlier in the year. But it is the same philosophy. Presti knows that Harden will be gone after the season, and he found a team willing to pay a premium for him. So, he is going to hope that he wasn't THAT important to the teams chances this year, and take the value for the future.