Be interesting to see any updated reports. We were last there Christmas 2017 and stayed at the Sheraton Haitang Bay. Like most places down there it was nice enough but despite 25-30c weather during the day the pools were freezing cold and not usable. Its unlikely we'll ever be back there but if we were during the winter we'd definitely be looking at places with a heated pool.
During the covid years we stumbled on an unknown place in central Guangdong called Hailing Island. Its pretty underdeveloped and rough around the edges but its got a bit of character to it that I've felt Sanya always lacked.