I had a different result on the experiment I conducted on water quality-but this might be due to the fact that I don't need to use dechlorinating products with my well water. Some of the dechlorinator can cause skewed test results for various reason-among other things.
On the experiment with 5gal unfiltered without live plants-I found that 50% weekly with vacuum would maintain water quality, however, I recommend a 90-100% monthly in addition to the 50% weekly- as a safety measure to error on the side of caution, since sometimes a hobbyist may not be able to vacuum well or correctly or have a lot of decoration in the tank or overfeeding or poor quality food related-But with proper deep vacuuming, feeding of quality foods properly- the 100% shouldn't be needed-based on my non-scientific
experiment, however, I did have a control tank.
I have found that too clean can sometimes be as bad as too dirty in some cases. Even in unfiltered tanks you need to maintain a balance-you have more going on than ammonia. You have both good and bad bacteria and by over cleaning you remove the slow colonizing good and this can allow the faster colonizing bad to take over-not to mention antibody development that is also important.
With the nitrogen cycle beneficial bacteria-these bacteria are self limiting-you can only colonize enough based on food supply, oxygen and surface area. When one of these are missing or limited they die and/or see spikes.
For example-we fishless cycle so that we can safely stock the community tank once the nitrogen cycle is established-If the only stocking in the tank will be a single Betta and we fishless cycled for-lets say 10 fish...all that extra BB with start to consume itself for food. Without a filter-will limit dissolved oxygen and in smaller tank you have limited surface area for the sticky BB to adhere to and colonize-This is over simplified-its more complex than that....but....hopefully you get the point...Read my Fish-in Betta specific cycling and water change recommendation for more information.