I see your point and I'm not disagreeing with you but here is and argument against your statement. I realize your frog is healthy and I think it's up to the keeper.

If you love your frog you should devote enough time and effort to at least change the water in its bowl. As well as having a fun time swimming around in his bowl he will also ALWAYS poop in his bowl so I don't need to scoop up poop from his main cage. And even though you say that it's better this way you also end up with more regular substate changes, more stress caused to the pixie by moving it around a lot, having to mix up the substrate a lot because of stagnant water deep below the substrate(I once tried your method exactly as you said to do it and if I were to dig down into the substrate with all that water at the bottom lying there undisturbed it would stink because of bacterial build up).