Well that way of training has pros and cons. If you intend to have 16 OD for example and the current OD is at 7, that means you'll have to train OD forever. Ofc when he's young, that's not a big deal but I think there should be some kind of balance. Also especially due to the positions of the training. You don't want a player to have atrocious passing when he's being trained on OD one position as PG. So I don't think training to the point you want it to be is the best idea.
However, that said, I do a similar sort of training. I'm not those managers out there who switches the skills often. I usually stick to one skill and train until when I judge that it has reached its sufficient level at that moment. So I have a similar approach in that sense.
I think SB is useful, but just not as much as other skills. But I do believe that SB is actually making some difference, it's just not evident in the match. Throwing in some SB training isn't a bad idea in my opinion.
Well you can still have a balanced SF at allstar potential. it's just that he won't be useful in higher divs because his overall skills will be too low. But even in higher div and in U-21 NT level, perennial allstar/superstar potential should do in my opinion.