I didn't say Portland was horrible at defending the three...I said the way their bigs defend the three's leave a lot of open three's as a result when the three is shot out of a screen or pick play on the ball by an opposing big. Besides that, IMO, you also can't simply base your gauge on the raw 3ptFG% of opponents. That's only part of the picture:
Portland is now 15th in the NBA in opponent 3 pt%. But they are 18th in opponent 3pt attempts & makes. That 2nd ranking needs to be better than the 1st one. That it's lower isn't good and it means they are giving up more points from the arc than their raw percentage implies
last season, they were 20th in the NBA in opponent 3pt% (not sure where you got 16th?), but they were 3rd in opponent attempts & 8th in opponent makes. That's the way you want those two numbers to inverse. It at least means that while their percentage is bad, they are denying a higher rate of attempts than most of the league...
....the thing is though, how much is Nurkic/Whiteside impacting this 2 year sample? and how much are Aminu, Harkless, Turner, and Curry impacting these numbers compared to the crappy perimeter defenders this season? Frankly, there's just been too much turnover in the roster to be able to peg one guy as primarily responsible for any one thing the Blazers are doing worse
Whiteside is leading the team, by substantial margins, in defensive rating, defensive winshares, and defensive box plus/minus, and he's doing it while mostly facing 1st unit offenses. He's the least of Portland's defensive problems
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in the Stotts era, ranking of opponent 3pt%/3pt FG's:
2012-13 - 3rd/6th
2013-14 - 11th/2nd
2014-15 - 6th/1st
2015-16 - 26th/15th
2016-17 - 27th/10th
2017-18 - 16th/7th
2018-19 - 20th/8th
2019-20 - 15th/18th
the first and most obvious takeaway: the combo of Wesley Matthews and Nic Batum was a really good pairing of perimeter defenders. But we kind of knew that didn't we? The massive downgrade in defense from Matthews to CJ is apparent (we also knew that), and while Batum wasn't significantly better than Harkless, he was still an upgrade. I think you also probably have to give Aldridge some credit for close-out ability on perimeter shots. Looking at those numbers, I think the Stotts perimeter defensive philosophy worked a lot better when he had Matthews and Batum
and Tince, I think your main observation is probably accurate: that being that Portland's 3 point defense hasn't been as bad as it seems. Made three's are really noticeable so the impression they leave when the Blazers are frustrating is probably heavier than the reality
if I was to just spitball a ranking of perimeter defensive importance, I'd rate it:
1) perimeter defensive talent
2) schemes
3) big men roles
sure there are other factors, but this is kind of what we're talking about...no?