Filtration doesn't do much to keep the tank water clean. The filter simply takes in toxic water and returns the water to the tank a little less toxic. A tank with a few fish in it, still needs large, weekly water changes to maintain a healthy environment. The longer the same, old water stays in the tank and is filtered over and over loses its ability support the fish and plants in a few days. By flushing a lot of pure, treated tap water through the tank, you replenish everything that keeps the fish and plants healthy.
Do the fish and plants a big favor. Change a lot of water and do it every week!
Filters, of course, can't remove anything dissolved in the water. So, if you are referring to the slow build-up of organics in the water, it is true that filtering doesn't correct that. But, filters do remove floating debris in the water down to as small a particle as the pores in the filter. Much of the faint cloudiness we can get in our water is floating particles. More filtering, with better filter media, does greatly reduce that cloudiness.
Filtering and water changes are two different things. You shouldn't select one and ignore the other. Many people are successful with both big, often water changes, and lots of filtration, just as many are successful with few water changes and moderate filtration.
I think most of us have observed the effect of a big water change on our fish - they get more lively, full of energy, and hungrier. So, I don't dispute at all the good effect of big water changes on the fish.