Special planted soil's do more than just add ferts, they can help with the levels of C02 in the tank and much more. Then there's the flora substrates which just add the traces, which again are fine. You just get the traces if any plants are lacking.
There is very little evidence, regarding root feeders, the plants pro's tend to think that the plants will tank from where ever they can. As plants are big opportunists when it comes to feeding. So...plants will feed from the root. But there is no such thing as heavy root feeders. If a water column is dosed correctly, there's no need for special substrates.