When one wants to understand what the fundamental difference is then we have to ask a question, what was the envisioned priority? Was it fauna with supporting healthy flora, or just flora.
In my case its hardscape based flora(low plant mass, easy to grow plants), the fauna of course I want healthy and they enhance the scape.
Cryptocoryne Parva has never been happy in my tank I suspect because I don't keep my lights very high (60 Par or so) or for a long duration(4-5 hours). The moss and Rotala grow annoyingly fast already.
But I still don't understand how knowing that differentiates EI from PPS Pro.