Hello Del...
Here's my take on a tank like this...
The filter has media and the bacteria living in the media, use a bit of the dissolved wastes that pass by, but not much. That's why any filtration system no matter how efficiently it runs, can't remove much of the waste in the water. The large water change, however does. I take out the old water with a lot of dissolved fish waste and replace it with new, treated tap water with no waste in it. The waste left in the old water that's left in the tank, dilutes to a safe level in all the new water.
If I remove the filter completely, replace it with a couple of air stones to still have sufficient gas exchange and increase the water change, I don't need the filter, because I've put in place something that will do it's job.
The large, frequent water change is the real filter and the air stone is the means of mixing oxygen into the tank water and allows carbon dioxide to escape.
B
For my tank it just would be either the same or worse. Don't get me wrong, I'm all for water changes and I do appreciate the tread as a very interesting discussion. I'm sure it could be done.
For my tank I know when I clean the canister filters the nitrates will drop. So I know the filters collect a lot of waste. I'm actually struggling with this at the moment as the canisters are off for 7 hours while co2 is on and I'm noticing it is harder to keep the water clean. Of course I'm a shocker at growing plants which doesn't help.
When I do clean the canisters they never seem overloaded. The bacteria are doing their job (both auto and hetero) - I'm just getting too much nitrates. So this is why I say I would end up at par - I would be increasing water changes to compensate for not cleaning the filter. In the past when the tank wasn't planted I found that even gravel vacs each week weren't as effective as a canister clean. The canisters are 10 and 20 litres each so decent sized filters.
So the filters are working and more filter cleans and more water changes would help but I see them complementing each other.
This is why I have shifted to a bare bottom tank for the small tank with fry so I could clean it better. Here I am almost doing this. The tank has a small hob (could use an air stone frankly) and I do large water changes and vac the tank bottom each week. Molly fry are fine with this. Neons didn't seem to appreciate large water changes so much unfortunately (but then smaller but frequent pwc's could still get to 75%).