I'm pretty sure most people won't be able to learn it, and the people I know, it took them about a years worth of GCSE music lessons trying to learn it... I used it for perhaps a week or two. Can't remember what the site was, it was significantly better than any others though.  I don't know who any of the people you mentioned are. I'm sure modes are useful, but not essential to use in a formalised way. My mentor doesn't believe in teaching jazz, or jazz theory, and he's one of the most successful jazz pianists/ innovators around.