How do we know players are limited in there own "mid-table" bracket until they are pushed to be higher then what has been expected of them to date? Look at Robertson or Ake for instance for instance, both where considered mid-table to lower league players, until they where in an environment that pushed them to be the best they can be.
And even if they are "Mid-table" players, we still need a squad, and if our base level of squad player is "Mid-table" we're doing alright.