When he, Sampson, and Balamou reject shots, we almost always get the ball back too, which leads to instant offense for us. That's what seperates the great shot blokers from the good ones, IMO.
Also, Obekpa doesn't need to get blocks to be a defensive impact. When he checked in to the Florida Gulf Coast game in the 2nd half, I saw nuemerous times where FGCU was looking to go inside (which they had success with up until that point), only to stop in his tracks because Chris was there, and pass it out to the perimiter. Almost always, FGCU didn't get as good a look at the hoop for the rest of the possession. Sometimes, just his presence underneath will be enough.