It's just a set of chemicals-fertilizers, quite the same as E.I., if I'm not mistaken.
You're right, if we talk in this way, There is no "method" of fertilization just a set of fertilizers (or chemicals) and people who dose x amount x day/week because it "works".
But the things that makes E
I, pmdd, ppspro "methods" are the ways that you manage your tank and how you deal with algae.
For example, those who use PMDD, if they get algae, the first thing they do is reduce PO4 (or increase if they read 0 after testing).
EI: check CO2 and do large water changes every other day.
Every "methods" has its limited agent. For pmdd are phosphates, for EI is the CO2.
If I'm not wrong, in the pmdd po4 weekly is around 0.2 - 0.5ppm (or a bit higher?), in the EI po4 minimum is 3ppm.
Some EI user front load macros, pmdd dose a tiny amount, of a specific chemical only when needed.
EI users do weekly 50-80% WC, pmdd users do only top ups and monthly (or bimonthly) WC.
Are these methods? For me yes because it's a way to achieve the same result, but using a different approach and a different way of thinking (but using the same chemicals)
I agree with much of what you say, but for people who are not very expert , like me, following a "method" can be useful as a starting point
