I never said that the 2ndary skills are not important, but are 2ndary. When your big man has 12/12/12 on IS/R/ID, then for sure you can train JS or what else you like. Being big men trainer JS is on my plans, but after this season.
but sometimes it wasn't bad to train the secondaries earlier, if you have the possibility ;)
Currently i am training a german National PF/C in OD, because he needs it and it sucks a little because i have to keep a eye on his game shape, too. So i play him one game as backup on his natural position and a full game out of position.
to train him inside skills isn't a good idea, because they will stop his progress.
Before i got him, i always train out of position, when i got the chanche to do it. And making rebounds/inside defence for my guards, in season break, or when i have games without a winning chanche.