According to nba.com/stats, only 35 percent of Aldridge's offense originates from within eight feet. From that same distance, Ibaka's rate is 46 percent. Meanwhile, Aldridge attempts 43.4 percent of his shots from 15 to 24 feet. Ibaka's percentage of attempts from that distance is 41.6 percent.
The Aldridge you see in Portland simply couldn't be the same Aldridge with the Thunder.
But Ibaka, so far at least, has been willing and able to sacrifice and play his role. That role includes some important defense that, while far from perfect, still gives the Thunder an interior presence and an intimidator that Aldridge is not.
Aldridge also isn't a consistent rebounder. His 9.1 rebounds per game this season were a career high and marked the first time he's averaged more than eight rebounds. So the Thunder wouldn't necessarily be upgrading there either.
Aldridge is a far superior passer and much more adept at creating for himself, and both of those skills would add a scary dynamic to the Thunder's offense.
But with Aldridge's higher price tag, his drop off on defense, his lack of postseason experience and his need to be the primary option, the Thunder is better off continuing with Ibaka.