It would be easy to prove me wrong. I've asked a lot of people to do it, but nobody has yet. Can you?
Ok. I'll go through and look at a few players (>700 mins/ season). I'll only look at WS/48 so it accounts for defense & is equalized for playing time.
Positives
* Nurk = 0.144 vs career of 0.113 (big improvement - but a lot of it is opportunity & maturity)
* Aminu = 0.090 vs career of 0.076 (big improvement - however his second best season was in Dallas in a similar role.)
* Harkless = 0.103 vs career of 0.085 (big improvement)
* Lopez = 0.166 vs career of 0.115 (big improvement)
* Mathews = 0.122 vs career of 0.097 (much better - but career numbers significantly hampered by injury)
Positives, but does it really matter?
* Meyers = 0.106 in Portland vs 0.096 in Miami (slightly better)
* Mario = 0.043 (highest of his career - but does it matter??? Hes not an NBA talent)
* Layman = Had 1 year of 0.111, but the rest of his career he has been almost unplayable.
* Thomas Robinson = 0.080 vs career of 0.053 (better)
Negatives
* Aldridge = 3 years in Portland under Stotts averaged 0.144 vs 0.175 in San Antonio (much worse). 3 of his best 4 years were under Pop (while the 4th was under McMillan)
* Batum = 3 years in Portland under Stotts averaged 0.110 vs 0.140 in Portland (pre-Stotts).
* Connaugton = 0.070 in Portland vs 0.139 in Milwaukee (much worse)
* Barton = 0.003 in Portland vs 0.094 in Denver (much worse)
* Curry = 0.082 vs career of 0.106 (much worse)
* Melo = 0.033 (lowest of his career) vs career of 0.123
* Bazemore = -0.008 (lowest of his career) vs career of 0.048
* Tolliver = 0.029 vs career of 0.088 (much worse)
* Babbitt = 0.047 vs career of 0.065 (worse)
* Mo Williams = 0.056 vs career of 0.080 (worse)
Neutrals
* Whiteside = 0.204 vs career of 0.199 (very slightly better)
* Ariza = 0.098 vs career of 0.095 (no difference)
* Hood = 0.080 vs career of 0.088 (slightly worse)
* Turner = 0.053 vs career of 0.051 (no difference)
* Shabazz = 0.091 in Portland vs 0.98 in Brooklyn (minimal difference)
* Ed Davis = Best two years in Portland (0.164 & 0.192) are almost identical to his best two years outside of Portland (0.164 & 0.191)
* Plumlee = 0.143 vs career of 0.144 (no difference)
* Henderson = 0.068 vs career of 0.063 (very slightly better)
* Kaman = Best year in Portland (0.112) is almost identical to his best year for Clippers (0.114). His second year in Portland was very poor relative to his career.
* Wright = Best two years in Portland (0.128 & 0.091) are his 3rd and 6th best years in his career
OK - After going through this excersize, here is what my take aways are.
1) We've had a lot of mediocre players come through Portland.
2) Both Aldridge & Batum played noticeably worse under Stotts than under other coaches (McMillan & Pop)
3) The shining examples of Stotts "helping players play to their strengths" are limited to Nurk, Aminu, Harkless, and Lopez. A strong argument can be made that Nurk's improvement was more directly related to situation than to coaching.
Stotts is adequate - but by no means is he anywhere near a 'top tier' coach.