Plants take up nutrients from both the leaves and roots, this is also true for terrestrial plants, but they have less reason to do so, still, they do have the ability.
Aquatics have a highly reduced cuticle, so they are really good at the water column uptake. If they have roots, then they will also take up nutrients in the sediment.
Do not fall this Steer manure..........use both locations, not "either or", "preferred" business, that's based on myths and poor understanding of aquatic plant physiology.
They are opportunist, they will take nutrients wherever they can find them.
So use both and that makes the trades go away and the method more robust.
Stem or Rossette plants, this does not matter, most swords/Crypts come from strong stream/river currents, they need roots otherwise they get swept downstream, they also need them when the water recedes during the dry season and when they flower. The roots also act as storage organs that allow the plant to go months without good conditions.
None of these traits and issues have a thing to do with whether they prefer anything as far as nutrients in one location compared to another.
Stem plants have the same issues, but address their habitat in a different manner, but they can be just as dependent on sediment as any Crypt or sword............
This is a myth.
Examples are excellent sword and crypts grown in plain sand with good water column ferts. And excellent stem plants grown in soil based sediments without any dosing to the water column.
Explain such results in this context?
It does not support such hypothesis and certainly not as far as dosing and aquarium horticulture is concerned. Using sediment ferts such as soils , clays etc is easier than dosing water columns, but that's true for all aquatic plant growing methods compared to dosing of the water column.
Wisest to use both locations, then the dosing of the water column is that much easier and then the sediments act as a back up. This obviously would yield the best growth also if you where to make a prediction.
So do that.