If I recall correctly, Hendrickson polled college coaches in 2013 and the overwhelming majority said they would pick Okafor over Alexander. I think the post you replied to had some revisionist history.
However, the Okafor-Alexander comparison and the Cockburn-Tseibwe comparisons are not analogous. There’s a big difference between Okafor (no. 1 recruit in his class) and Cockburn (high 4 star recruit). With Okafor, the immediate production was much more assured than with Cockburn. Also, Alexander was only about 6’8” and undersized for a center with no outside offensive game (though he did have great athleticism). I believe Tseibwe is 6’10” (I could be mistaken), which is more ideal for a rim protector. I think Tseibwe’s immediate defensive contributions as a rim protector and glass eater are likely to exceed Cockburn’s immediate offensive contributions. I also think it’s easier to integrate Tseibwe into an offense despite his possible skill limitations than it is to integrate Cockburn into a high pressure man to man defense. All this is to say that I dont think the risk with Cockburn is as low as you make it out to be.
Oscar I believe is more like 6'8" and mobile, I don't think other than 24/7 that he has ever been listed at above that...maybe his growth plates are still open?