This is just a game, and at the end there is always a positive side. I have played enought LEAGUES With my teams to know that.

If you have a strong team average Q of 5/6 stars forget the CUP, because you will face to many stronguer teams, but you probably Will be good in CL and LEAGUE.
Getting out of the CUP early, means that you can play a friendly each CUP day, winning money, boosters and giving extra training to your subs, you also save greens because your main player only have to play one game and the friendly can be played any time it would be more convenient to you.

The same thing apllyes to CL, you play the 6 group games, get your money, and then 1 friendly each day.

If you start to get trolled in LEAGUE, no problem, you probably Will finish top 4, and like Quambu said, there isent any big diference between 1st and 4th. If you finish only between 5th and 7th you still promote and get a prize money, being out of CL, means playing more friendlies, and saving greens, because playing only one game per day, means less greens and reds needed, that can be apllyed to extra training, stronguer team, more likely to win the LEAGUE.

Even If you are really unlucky to finish out of top 7, at the end of the season, your players Will not lose any star, meaning they Will became stronguer for next season, you dont get any prize money, but probably you dont need to buy any player, saving money and tokens, you can even sell one or to players to cover the lost of income from CL, less games, are equal to less players needed.
More greens and reds to apply on training, stronguer team, more likely to win the LEAGUE.

At the end no matter what, you always win in some way.