I still think though that if one uses “win shares”, generically as you did (I believe) or as B-R WinShares following Oliver’s formula, then one is estimating total player impact and my main and basic point is that I don’t think boxscore stats alone do a very good of estimating defensive impact because it misses individual impact on shot defense, the largest / most important part of defense. Thus, my suggestion that the model does a better job as specified with offensive predictions than defensive impacts. That was the point I perhaps rushed to make and not so cleanly.
Yes. Whatever errors there are in the "valuation" metric will naturally hurt the validity of the model. Winshares is a flawed measure of individual defense in particular, so the model may not predict defensive impact as well. Basically... it is predicting win shares not "true" value. Separating offense and defense would be difficult however. Since it is looking at total win shares across a season not a rate (like WS48) one implicit factor is "minutes played", which will be a function of both offense and defense and will impact total defensive and offensive winshares simultaneously. I have also made a version of this model using RAPM-WARP. The results were largely the same, but obviously with some differences. Of the 2013 class the most notable difference was that it didn't like Olynyk nearly as much... that would be consistent with the idea that WS doesn't appreciate defense as well. I'm using the WS version because I have WS data back to the 80s, but not RAPM data. I decided the benefits of a bigger dataset outweigh whatever accuracy RAPM adds over WS.
In 2012 Anthony Davis is estimated to have almost as much chance of being a star as all the other members of that entry class combined. Only 6 other players given more than a 5% chance to be a star.
John Wall given tied for the highest chance of being a star in 2010 class but less than 40% of the chance given to Davis.
Not sure if you are pointing these out because you find them dubious or not... but they seem pretty appropriate to me. Davis is the second highest scoring player in the past 30 years on the "expected win peak" measure. Only Shaq beat him with a 18.9. Shaq also had an even higher 75% chance of being a star... Interestingly, if he had left after his sophomore season it would have been over a 90% chance (he was that good at 19).
I also like that Kawhi and Faried are really high starter likelihood but low star. It is consistent with the fact that they performed well collegiality in statistics that are highly conserved between leagues. They are "we know who they are" kind of guys. Kahwi has a solid chance of eclipsing 10 WS in a season before 26, but only because he unexpectedly developed a shot, and I wouldn't bet on it anyway.
It didn't like Barnes, but Barnes also had a pretty pedestrian season by WS.
Missed on Drummond to an extent, but the model liked him a lot more than I personally did before the last draft.
Definitely missed on Bledsoe and Bradley... going back we could add Westbrook and Deron Williams to that list. It also hated Nash (1.9 win peak expected.) The model completely whiffs on future star point guards occasionally... however the point guards it likes have an excellent track record:
Only 3 misses in the top 30 (Will Avery, Tony Delk, and Lee Mayberry... and then Jay Williams, it even hits several future stars who hung around until late in the draft.
The most consistent pattern of misses I have found is shot-happy tweener forwards. Beasley, Derrick Williams, Glen Robinson, Donyell Marshall, Antoine Walker and probably some others all scored extremely well on the model and then failed to different extents. It is true that NBA teams overrated all of these guys as well, but not to the same extent. This would be a good reason to take Anthony Bennett's rating with a grain of salt or two.