Absentee owners absolutely are renting their units. Where have you been? Lots of long-term rentals, both single family home and apartments, at least on O'ahu, are owned by landlords who do not live in the units. Some of those owners are individuals and corporations on the mainland. The last apartment I rented when I still lived there was owned by a mainland company. The apartments in the building (24 floors) were not all owned by one company or individual, each was owned separately.
The subsidies you speak of were funded by the federal government through COVID-specific legislation, and was not unlimited. They distributed a certain amount to each state to administer. That overall took a huge sum of money, which as a country we cannot afford to spend every year. That would be hundreds of billions of dollars every year across the country. Hawaii alone received $200 million. You raise property taxes enough to raise $200 million every year in Hawaii, you better believe it will come back to bite regular people in the butt, not just rich people or companies that own the properties. Plus, if you raise $200 million (or any amount) in property taxes from the owners of rental properties causing rents to rise, and then give it to the people who are renting those properties, it just goes right back into the pockets of the owners you took it from in the first place, so the money is moving in a circle for no reason. How is that benefitting anyone? You really, truly don't think about or understand the second and third order effects of your proposals. The good idea fairy is alive and well in this one.