The Rams simply do not have enough elite players. Donald and Kupp are the only true elite players that they have.
Ramsey is very close, but he's wildly inconsistent and can't even catch a football.
Stafford is also very good when he gets in a rhythm. Matt Gay is good too.
That's all the Rams have. Bobby Wagner is not elite in his present form because he simply lacks the physical proficiency that he had 4 or 5 years ago.
You will find that good NFL teams have at least 3-4 elite players during any period of playing unquestionably outstanding football.
This is the way of things.
