I never said it was "optimum", it's just not neglectful. I also never claimed oxygenation was the only factor involved in considering water quality (I'm well aware of the nitrogen cycle) just the only one I mentioned. Yes, maybe I should do 2 or 3 water changes per week instead of one to compensate for lack of filtration, but I should also eat better and contribute to charity more. These are all arguments of standards. Nothing's perfect, even in a "natural" environment. Nothing about keeping fish in an aquarium comes close to natural really so don't let the crown weigh too heavily.
Yes maybe you should eat better and contribute to charity, but that is your choice not to. I think you would have a different outlook if you wanted to do those things and someone prevented you from it.