I don't have an agenda to disprove IP. I want to live in a universe where it works, but so far it really seems like we don't. I hate to raise the spectre of UFC because I know you guys hate that. But millions of dollars, multiple careers and issues of national pride rest on the outcomes of those matches. And sorry, but they ARE the best comparative test of martial arts we have available. They scrape for every microscopic advantage they can gain. They generally deride IP and that's the most credible opinion I know of.
I trained for about 6 months with someone who's a (possibly self-) titled IP Master and finally concluded it was a crock. I chalked that up to individual experience, not to reflect the issue as a whole. I wondered the same thing about Aikido, started training in it and 9 years later, I'm still enjoying it.
Not everything I learned here "works", frankly, but I know the difference because my 24 year old, 2nd kyu son outweighs me by 30 lbs and cuts me zero slack. If I think something works, he loves to make me prove it.
And yet...there are no scientific comparisons, studies or data with a clearly demonstrated advantage for training in Yoshinkan - why doesn't that cause a problem for you?
For that matter, the UFC generally derides most traditional arts, including Aikido (even Yoshinkan Aikido) - so how come you don't follow the "credible opinion" that you yourself are citing?