It will cap the dirt fine, by light I think people mean that its kind of annoying to plant in, and will can be difficult to plant stem plants in, since it has such a low density and the plants are buoyant enough to float out.
I have three inches of Eco complete in most of my tanks and find it easier to plant than regular tank gravel and fine sand. Easier or harder comments are all relative and prove to be meaningless without clarification or supporting information.
Any type of planting in the aquarium requires proper tools or know how. Dirt kicks up a dust storm which settles in time. Packing eco substrate with sand would allow for a denser substrate.
The Eco cap of two inches would be fine however anyone who reshapes often would eventually be left with cap breaching and a mess over time so expect it to happen... More so when the roots of an established plant gets displaced.