"historically it hasn’t necessarily been that premium."
Premium should be judged by the product not the brand. You would expect most places would convert down not up, the opposite here.
This is a country that Courtyard or Four Points would put most of Marriott or Sheraton in North America to shame.
To be fair, Phuket or few other Thai islands are already expensive compared to Thailand standards. So one might say, it's already premium.
This particular property definitely shows some aging, but I would say if it's called a (US standard) Ritz Carlton today, I could barely tell the difference.
That being said, what I don't think this is RC material would be the beaches, too much elevation, and your fellow guests (likely change after the rebrand).