IMO you are thinking about this wrong. Unless you're flow is too much to the point it damages plants, it kind of doesn't matter. Especially with fast growing plants like stems, they will consume a large percentage of the waste, if not all, hence why we need to add fertilizers.
With that, a filter will most likely have the highest concentration of bacteria, but between soil and other surface areas in a planted tank, most reasonably stocked tanks can get by with what is in the tank alone plus flow. I have successfully had a 7 gallon cube with dense crypts, moss, and over 60 trout goodeids. This was not optimal, and I didn't even realize i had that many, but the tank and fish were healthy with one of those azoo hob filters with a little matrix in there and the aquasoil. They have since been moved to an 80 gallon.
One of the biggest benefits for me with having excess media in my sump is the ability to spread out the bacteria. This allows me to insta cycle a new tank, for myself, a QT, or to get someone new into the hobby. But in removing that media, I am not shocking my system. Additionally, as you tank ages and stuff gets dirty, there is a buffer zone.
Back to flow, the way media works, is it is porous. So even if water hits it at speed, only so much can flow through it so quickly. And while saltwater and freshwater bacteria are different, my bacteria in my reef has no problems handling my tank at 100x turnover. Even a FX6 is pumping 500gph or so through a 5 gallon bucket, so 100x turnover give or take for canisters. All of these combined are why I believe high flow with regard to the filtration process is a largely irrelevant question in a real world aquarium setup.
