I agree with you in this sense.So not a Sane replacement and a completely unnecessary buy when you consider how good Mahrez has been on the right and we also have Bernardo and Foden.
He isnt a DIRECT Sane replacement on the left, as in run behind and left foot cross in box, but that he can play LW at all.
But him on the right and Sterling left is still good, Sterling scored alot of goals. You can help recreate some Sane-esque goals by using Foden and Mendy on the left with Sterling.