He has not been at his best but that is his position imo. Mahrez will never be a right winger ever.Bernado largely flatters to deceive out there and rarely beats his man, not a right sided player in a front 3 and will never get the goals or assists we should be after from a players out there(Sane, Sterling, Hazard). Sterling trying to force things from out there simply meant coming inside constantly where it was already congested.
Sterling may well eventually play down the middle.
I am not sure really where you are coming from because Bernardo and Sterling have been exceptional as wide forwards. To say they are not suited to these roles is to ignore the last 18 months.