The Warriors is an impeccable credential for this sort of film.
However, were someone needing a mentor figure in a Space Opera or Urban Fantasy to look at the Rolodex Card marked "Mark Hamil," would he think the original Star Wars trilogy, or would he think Guyver I and II and Wing Commander, The Movie?
Let's face it. The number of A or even C list American Actors with Martial Arts backgrounds is at a low point compared with the '70s and '80s. The David Bradleys, Billy Blankses, Michael Dutikoffs, and Steven Segals of that era are an aging and dying breed nowadays.
And Shia LeBeof is no Ralph Macchio or Jason Stillwell.
These are not parts someone could be trained for in six months, even with the likes of Yuen Wo-Ping or James Lew doing the training.* This takes at least three years of training with a teacher and sparing partners to support it. I ought to know, as I have spent the last eight years studying European Longsword and Sword and Buckler with only a few printouts of period manuals, John Clements' Medieval Swordsmanship and Christian Tobler's Secrets of the German Longsword, and after an average of four hours a week I'm still not particularly good if I say so myself.
*of course, you could get a non martial arts background actor for this part, but then it would look hokier than the live action version of Fist of the North Star.