I tried that the last 3 months with my new club (level 5). I won the treble twice and lost the CL final once. Most of the times, there are 1-2 other good people in your cup and CL...
I always kept 6 strong, trained players and 8 weak ones, so the 2 star youth players or 3 star players I bought in level 2 which are now 1 star.

It is a crazy strategy, you can put up insane statistics (one of my players scored 102 goals this season and I won every single game) and I would also maybe recommend it for beginners to build up a few ressources like green packs and tokens, as you dont even need that many and sail smoothly through your competitions, while also building up your training level, finances and so on.
On the other hand, and thats why I would never want to do it with my main account, its just boring. You don't need to attend matches, there is no excitement about the games you play as you will win almost every single one as long as you have your bonuses up.

So I will probably do it for another 2-3 seasons and then go ahead with 11 trained players and try to dominate other active managers. Good thing about this is, you don't harm anyone with it. 99% of the teams you play are abandoned and inactive, so you are not unfair and take the fun away from them by absolutely destroying them.