Let's look back at some history: PMDD:
https://www.thekrib.com/Plants/Fertilizer/sears-conlin.html
Frankly PPS is blatantly plagerizing PMDD.
"Edward" never once acknowledged anything he took and posted to the original authors of PMDD.
PMDD predates PPS by 8 years.
I know both authors for PMDD as well as the PPS folks whom we have never seen a last name nor their own tanks.
PMDD suggested using test kits to balance, but did not forgo the water changes at 25% weekly or thereabouts to minimize any build up.
You can see the infinite series used for dilution with partial water changes using Fe as the nutrient in question.
EI is about 90-95% PMDD. It's more a simplification of PMDD using water changes, I fully understand that the hobby is more an issue of human behavior and social issues rather than "Science" or water test kits.
Getting folks to test is a rough arugment to make. Some will do it for a little while, then stop. Other's will test only when there's an issue, not when there is a good success. Actually they should do the opposite. Think about that one for awhile.
Non CO2 method use no water changes as the rule, but many fail as they only treat advice like a cafeteria, they pick only what they WANT and leave behind all the caveats and good advice they do not.
Same with testing.
And same with doing frequent water changes, but that's easier for most than testing consisently.
And my non CO2 tanks, as well others who scape with them at higher level rival most CO2 enriched tanks. So why do water changes or add CO2? CO2 is poison right?
Not good for fish or shrimp etc? If you want less work/labor, input, then that seems like a better option. No testing other than TDS if you want.
I made this point to Edward, God, 12 years ago? Ecology, waste, balance, all that was mere rubbish I guess.
Dosing? Why not just use ADA aqua soil? Add a tiny bit to the water column, replace the soil once a year?
No test and the plants do great. You do water changes in the start, but after 1-2 months, none are done typically.
Or you can do EI. Or a modified version thereof.
Is rich PPS like light EI? They add the SAME things after all. And given different plant species..............densities, light intensities, CO2.......it makes sense you have success with either method, plants STILL grow. Even without CO2 and a non CO2 meoth, plants STILL grow. Ergo, much of the claims are based on a weak premise.
EI serves a good purpose to make the aquarist tank independent of fertilizers. Thus the aquarist can then focus on mastery of CO2, argubly the most important factor if the gas is used for anyone worth their spit.
If you can do that, and you can do a non CO2 tank, everything else.............. falls somwhere in between.
BTW, I have 4 tanks that get CO2 gas, and no water changes, they also grow some of the touchinest plants I am aware of. While not "scaped", I see no reason why they cannot be.
So I use several methods, as I have several goals, but generally, if I scape and tend a tank more, I want it to look its best, thus I am much more likely to do frequent water changes and keep it cleaner.
So if you are honest about learning more, they perhaps learning each method is more the game plan, not just one. They all do the same things and add the same things, just at different rates. So they are NOT THAT different at the end of the day.
People's habits? Those are the real evil, hehe.