Many fishkeepers, including those with heavily planted larger tanks only use/need minimal filtration - some even just use a lone HOB or sponge filter. Plants can do an amazing amount of filtration and if allowed, decaying detritus will organically feed the plants (as it does in nature).
Not so. Like any filter that draws water from near the bottom and returns it on top the flow dynamic studies show us there is significant circulation. Also, as we've discussed, unless you use ultra fine sand with an inlet tube too low, sand is not an issue. I recommended the HOB's for mechanical filtration because of the relative ease in servicing frequently to remove the crud. (I'm not a fan of cartridge filters alone, but for mechanical filtration only, a cartridge can be swapped in just a few seconds. [although I think I'd stuff it with polyester fiber])
We do water changes to freshen water and simulate rain like nature.
There is a thermal gradient in nearly all bodies of water. I think our aquariums are typically much more uniform in temperature control than many/most waters in nature. I guess I'm not sure what 'heavy buildup of things on the bottom' you are referring to.
Any fish keeper who runs heavily planted tanks knows the value of having good water circulation. I'm not sure we are on the same page when it comes to minimal. Minimal means enough to keep the water moving yes? Any time the water stops moving in a tank you get a problem.
Not all filters are created equal. What they are capable of doing changes depending upon the set up. Different tanks have different depths, widths, lengths...etc. The situation and set up alters how efficiently different filtration systems will do their job. A quick aside, I'm not sure the water fall feature of many HOBS are healthy to a planted tank...but that is often debated and is better debated elsewhere as it is off topic here.
Aquariums are always closed systems. So it is up to us to identify what needs our hand to try to simulate what needs to happen. So while we heat tropical tanks, and do water changes to simulate the exchange of water and movement of water in nature, we also run filters to filter water, and move water to simulate current.
Current is part of a sustainable healthy water system. It occurs in open and closed lakes, rivers, streams, and the open ocean. It forces warmer and colder layers of water to mix...and forces the up-welling of nutrient laden waters. The layering is healthy because the water is always moving aided by a current. You are getting exchange and therefore no dangerous concentration.
While it is true in many tanks our water is very much uniform...that's not always the case. Larger tanks can have a harder time at being uniform if current is not set up to carry your heat around. Deeper tanks can also begin to see thermal layering. There are some pretty impressive DIY projects I've seen where I cannot believe there isn't thermal layering potential there.
The kind of layering I am trying to communicate has more to do with layering of sediment/organics. Even if your water is mostly unform in temp you can still get a layering of heavier water at the lower area of your tank. There is only so much your plants if you have them can take in before that becomes an issue.
In a closed system if you have layering but no effective exchange you create a stressful system for the fish to live in.
Hang on Backs can create situations where only your top layer of water is being efficiently moved/filtered. Hence why I suggest to people who run long, and deep tanks (large tanks) to consider other options. If your intake doesn't go far enough you down you have to either make it go down further, or consider other options.
I for the life of me cannot understand buying a large tank, and not investing in an intelligent system. Make your current complete so you don't have issues down the road. HOB maintenance gets annoying after a while...so to the OP save yourself the grief. Don't buy an HOB, as it'll find its way to your garbage can. So you are essentially throwing away money.
