See, while I think it would be inefficient, we don't have any real info on how inefficient it is, if any. In my view, if you could train 6 guys to the efficiency of 95% of single position training with an advanced trainer then I think it's actually a good idea.
It really all depends on what your goal are though. For a team trying to be completely home grown it could be a good idea to get the most amount of players the most training.