Another point is I earn less in L5. The opponents’ players are actually low % and easier to train and improve. I’d rather to be promoted to L6 and receive 2 star loss if Nord wants to balance me.
And there you go. You've figured it out after 5 seasons. Well done. But there are others who will be suckered into spending real money season after season trying to play catch up to teams a level above them in the cup and champions league. That's what keeps the game online.
As for yourself? You need to decide how and if you want to play remembering that you will always be penalised for success.