So, what do you think Ryoshu's 'purpose' was?

I initially thought it would be to give the Fingers a unified leader, make the Five Fingers a Hand, then I thought that it was simply for prestige (Valencina explicitly says it'll bring her back to the Thumb's good graces)
.... but Matthias seem to be on good terms with Ricardo, so he's not an exile either, and while he mentions he's not in his "prime", it also doesn't seem to bother him that much (and again, he seems on at least okay terms with the rest of the Middle).