This misunderstanding seems to come from aquarist believing in a hard separation of mechanical and biological filtration. Fundamentally all mechanical filter media can act as biological filter media as beneficial bacteria (both heterotrophic & autotrophic) simply require water flow + surface area to attach onto and grow. Additionally, bacteria typically do not grow into standalone colonies, most micro-lifeforms have various co-existance relationships and in this case both will live in the same colony. We do not use mechanical and biological filter media interchangably because mechanical media either has enough surface area but is not porous enough to allow water to flow through or the reverse -> bacteria colonies either further clog up the filter or not enough surface area to grow effective colonies -> tank won't cycle properly. Thus, mechanical media is usually reserved for "polishing" the water quality by removing visible solids but not necessarily biological filtration.
This is why the best biological filter set ups use sand, beads, or kaldness media; they maximize surface area while also allowing for water to flow through/around them for tumbling or even in static formations. Thus, most of the heterotrophic bacteria will still be on your biological media ergo why "overfiltration" is a little bit of a myth but there definitely needs to be some cost-benefit analysis done to check if it is worth it compared to just more water changes.
