My opinion is that your team need investment. Those 4* players, who were 5* few days ago, now they don't have enough quality to face teams with 5* players.
I 'm not saying that the 5* players you will buy (if), gonna perform great, but whole the team 'll be more competitive.
For me , (except formation) quality is very important.
Great quality (stars) gives victories > rates to players.
One -two 4* players still can help the team, but more, it's risky.
Of course it's a must, the right formations/moral/condition of the players.
Also check your win bonus - i don't know if and how it's affects but make some tries.
Also