I've proposed the idea to merge both modes before, but one must be considerate in doing something like this because the only reason that casual is so popular is that there is no rank nor pressure inside. If you start adding leagues (bronze -> crystal) into it, I can guarantee you that you'll make half the players flee the mode in less time than it takes for the devs to nerf Bard to the ground.

You'll need carefully hidden ratings from some form of ELO system where everybody can only see theirs and not anybody else's, unless for example they reach a certain threshold (crystal level) where it becomes readily available for everybody to see, or something in that vein, for example.

You also cannot rate performance on all the metrics shows in the tally alone, else you'll favor immensely certain jobs or roles over others (good luck shining in such a metric based system as a support job like BRD).