I do agree that there can be an advantage with changing stack sizes if your opponents are not adjusting properly to the effective stack size. However, it's difficult to quantitatively gauge what that advantage might be in terms of winrate, and this advantage (or disadvantage) varies in magnitude for everyone.
At CAP I get roughly 20% more hands/hour than I did at the 20-50bb tables. Does this equate to a 20% increase in profit for me? Perhaps it's CAP is more advantageous for me because I am one of the best 20bb players out there (and not one of the best 30bb players). Perhaps it's less beneficial for me because I can't get deeper with fish. But then again perhaps 20bb CAP is better for me even though I can't get deeper with fish because I no longer have to worry about being outplayed by someone that is a better at 25bb, 30bb, etc than myself.
I think what I'm getting at is one man's trash is another man's treasure.. one man's pain is another man's pleasure. Even though we are both implement a short stack strategy, CAP may not be playing to your strengths, but that doesn't mean that they aren't playing to mine.