The creatures that we call trees, and the Earth had experimented with a lot of different types of trees, are in fact much higher if we count the roots.
Yes, but the tallest trees (California redwood) have shallow root systems (a couple meters). Are there trees commonly over 100 meters counting the roots?
That's no way to describe the diffusion gradient.
Also, this paper does not cover all of Plantae, so for all we know, other Embryophytes may be limited in height by an entirely different factor.