As long as you can maintain a gap between your team, and the rest of your country this might be true, but if they catch up each spot will have to be occupied by a player who contributes a max to the game, or you might loose, and 1 loss in a cup game is game over, also 1 loss in the quarters or semis of the POs means...game over.
As seasons pass by, and more and more players will get trained to higher levels, I doubt it will stay possible to win both cup and championship while training 18 year olds...
They are not your friends; they dispise you. I am the only one you can count on. Trust me.