My aunt has 2 Oscars in a 75g bare bottom tank with just a small HOB filter. The only thing in the tank is a piece of 10" diameter pvc pipe that serves as a hiding spot. The Oscars have got to be at least 15 years old and she claims that she has never once done a water change, just tops it off when it's low and scrapes any scum/algae off the walls occasionally. She also does not check water parameters, and tops it off with tap water without treating. The fish seem to be extremely healthy. She has a half dozen other tanks, from 10-55 gallons, many established for 5+ years that she maintains (or doesn;t maintain) the same way. May be dumb luck, or may be we're too worried with water parameters.
I personally wouldnt run a tank that way, but she does and it must work because she never seems to have any issues.