If you establish successful young players and keep them from season to season, your chances of winning go way up.

If you're having to replace most of your team each season, you're likely going to struggle and perform worse than you expect.

I've only won 1 cup, and got 2 troll results in my favor vs the same team. I played a team that was 10 quality points higher, his whole team was 7 or 8 stars to me, played the 2nd leg without my 7 star MC, and beat him both matches 2-1. How do you think that guy feels?
I have to remind myself that the Triple Crown banner is lit up on my trophy case largely because of that when I get angry or frustrated at the silly results. Some great managers from my FB group who have been playing a lot longer than I have and know much more than me do not have any cup wins.

At season 9, I have several players who have been on my team since season 6 or earlier. Establish this base of reliable players that can improve quickly, and that's your best chance to win cup without intentionally weakening your team.