Every skill is useful. I am not denying that, but some skills are much more useful for a certain positions. Why waste your training for a team training that is painful slow, and not focus to develop fast the young/good potential players that you (maybe) have? Even on zone tactics for example that u r guarding space the big men staying inside, they are not hunting guards outside. You can have valid point if we talking for PF's, as my PF has promiment IS and same on JS, but i rather 1 pop up more on rebounding for example than on OD.