Your misleading people Manon or just omitting things.. You cant train a whole team in the top level and be effective. You can only train 1 single player. Training a team in a league is about substaining merit of equal strength or equal play.
I have six players of my nine (well, ten now) player rotation that I trained since they were eighteen, and I'm far from the most effective trainer. You can train three players at a given time in full single position training (though of course it's more reliable to only have two and a third guy who gets minutes when things work out right) or six if you do two positions (or five fairly reliably).
It's very hard to train from scratch at a top level, of course, as long as you want to also compete in the league (and of course the Cup as well). I was able to do it in III, didn't even bother trying in II - I finished up my big men, finally got my FT training where I wanted it and now I'm just using a level 2 trainer and training rebounding or SB to avoid having any more team training whenever possible to minimize the chance of skill drops.