It's not inconceivable that there's some boundary effect. Probably there is -- like the often trotted out "spacing" effect. That too has to be there. But, these effects are secondary & minor, really minor, as it would be possible to show via statistical regression (& probably has been).
As well -- just as in the case of the spacing effect -- those measurements you cite are not a "with Rui" vs. "without Rui" data set. When Rui is in, someone else is out; when he's out, someone else is in. Different lineups for that matter. Really you'd have to find data for every possible group of 4 w/ whom Rui plays, then measure that group with him in & with him out -- but that 2d measurement would have to be taken for each alternative to Rui. Oh, & you'd have to regularize for the varying opponents & their overall rebounding.
Pretty close to impossible. Not to mention that, for any of these individual measurements to gain any trust, they would, every one of them, have to be based on a sample set that warranted confidence. But... it's unlikely that many (any?) would be large enough for that.
All that on its own is enough to make this a pretty worthless pursuit. But... there's something more important & much more basic that underlays it.
Tell me: are we going to be able to judge, to any meaningful degree, how good a player is? If so, we have to give him responsibility for his numbers -- credit where he deserves praise & criticism where that's what he deserves.
I note, for example, that you weren't suggesting that Rui's improved TS% was a function of what some other players were doing! When you describe him as having improved, you give
him credit for his improved 3-point shot. & that's how it should be.
IOW, this perspective is trotted out to explain away a weakness. Really, just the obvious motivation of the line of thought should suffice to make one drop it.
Moreover, Rui doesn't need the help!
He's improving, which means, most importantly, that he
can improve! He's capable of it. That's an important thing to learn about a rookie! It's the 2d thing you hope to learn, the first being that he's capable of playing in the league at any not-disastrously-low level (which Rui showed right away).
Does this mean that nabbing Rui will turn out to have been the best thing to do w/ the asset we had? The #9 pick? No, it doesn't. It is almost inconceivable for it to turn out that way.
But, that's irrelevant. That's about how to manage the draft, how our FO managed the draft. Not about Rui.
Nor is it equivalent to handing out an "F" to Tommy! Not when Barrett went #3, Hunter #4 & Culver, Garland & White followed. & not when 3 minutes after we took Rui, the geniuses at Atlanta followed up their pick of Hunter by taking Cam Reddish.
Now, that gets you an "F"!! Then look at all the trades they made to position themselves properly to p#ss in their own soup before sitting down to lunch! Good God!!