I see what you're saying but I don't agree. Detectable ammonia and nitrites in the water are materials the bacteria cannot consume at the moment. While multiple conditions can affect bacterial growth many of the big ones are highly stable in an aquarium, the temperature isn't going to vary by more than a degree or so, pH is steady, flow is steady, etc. The only thing that's changing is ammonia or nitrite in the water which is built up excess that they cannot consume. The bacteria are already consuming food and making more bacteria as quickly as possible. While there could be other factors we don't monitor that are changing in a semi-closed system like an aquarium they are minimal.
Since what we're looking for is a sufficent number of bacteria to consume the ammonia and nitrites at the rate they are created in the aquarium a sudden dramatic rise in the number of bacteria to a level sufficent to consume 0.25 or 0.50 ppm of ammonia or nitrites rapidly would be the tank finishing cycling. If the bacteria populate enough to consume all the ammonia present in a tank your tank has cycled. If there are not enough to keep up with the fish they will not be able to eat themselves out of house and home because they will never able to keep up with production.
Look at it this way. Your tank is a table. A conveyor belt is bringing a constant stream of food to the table. A guy is sitting at this table eating as quickly as he can. The downside is to begin with he can't keep up. The food starts to back up on the table. New guys get added to the table from time to time but the food keeps piling up. Eventually someone comes along and takes away half the food piled on the table. Well the food doesn't stop coming, and the guys don't stop eating.
Here's the thing, the pile of food on the table, the ammonia and nitrite in our tanks, they're byproducts of what's really important. What's important is that conveyor that's bringing food to the table. If the guys around the table can keep up with it no food piles up. If they can't the food will pile up no matter how much of the excess you remove. I can remove 99% of the food from the table, but if the guys around it can't keep up with the conveyor they still won't be able to clean the table off. You see the conveyor keeps working at the same speed no matter what. It doesn't care what happens on the table, it keeps bringing the food. In our fish tanks our fish don't care what's happening with the ammonia levels. They keep on breathing, eating, and pooing no matter what. Their production is constant, until you have enough bacteria to consume all that waste they will never be able to remove all the ammonia and nitrites from the water.
Therefore water changes make no difference at all on cycling the tank. If you don't have enough bacteria ammonia levels will alway be > 0 and always on the rise. If you have enough bacteria to consume all the waste being made then guess what, it's cycled.
Like you said though, this is mostly academic because it makes no difference to fishless cycling where there are no fish requiring you to keep ammonia levels down. I do think it matters somewhat though because I have heard people hold off on water changes with fish-in cycling, or advise holding off on them, specifically to keep from prolonging a cycle. I think it's worth pointing out that it doesn't, and to keep on with the water changes for your fish's health.