To test this hypothesis I looked at the slugging% of players who were with the Twins in the Gardenhire era and then joined other teams. I am comparing their SLG% their last year with the Twins with those of their first year with another team and 3 years removed from the Twins. If the hypothesis is correct there will be a significant rise in SLG % when left the Twins at least by 3 years. The list is for 150AB/year minimum.
Here is the data:
Batter SLG@MIN SLG@MIN+1 SLG@MIN+3
David Ortiz .500 .592 .604
Jacque Jones .438 .499 N/A (2008)
Todd Walker .397 .459 .431
C Guzman .384 .314 .446
Dustan Mohr .399 .437 <150AB but .466 MIN+2
Bobby Kielty .400 .370 .441
D. Mientk .363 .407 .440
*AJ Pierzynski .464 .410 .436
Matt Lawton .415 .399 .421
Brian Buchanan .415 .455 <150AB
Casey Blake .250 .411 .438 (less than 150AB @MIN)
*Corey Coskie .495 .398 out of baseball
Shannon Steward .368 .394 N/A (2009)
Chris Gomez .354 .346 .439
Javier Valentin .381 .356 .520
From the 15 players listed the only 2 that do not follow this hypothesis are AJ Pierzynski and Corey Coskie (and Corey was out of baseball at the second data point.) How big is the difference? The average player including Coskie & Pierzynksi, raised their slugging percentage by 16 base points they year after they left the Twins and by 65 base points the third year away from the Twins organization and hitting philosophy.
I think that the data certainly supports this hypothesis...
Part 2: looking at the newcomers into the Twins organization
Here is the list for the players who came into the Twins organization from others during this era. I am comparing their SLG% the year before joined the Twins with those of their first 2 years with the Twins. If the hypothesis is correct there will be a significant drop in SLG % when join the Twins at least by 2 years. The list is for 150AB/year minimum. The sample size is smaller because the Twins do not usually bring established players into the organization:
Batter SLG@MIN-1 SLG@MIN SLG@MIN2
Shannon Steward .459 .447 .388
Juan Castro .378 .386 .308
Luis Castillo .374 .370 .352
Rondell White .489 .365 .321 (<150AB)
Tony Batista .455 .388 N/A (not with the Twins)
Jeff Cirillo .414 .327 N/A (not with the Twins)
Clearly, the data show that if not by the first, by the second year a player from another batting philosophy joins the Twins, his slugging % will suffer measurably.
The data speak... It is time for a change in this philosophy