Let me pose a question to you all.
There are 2 main commonalities with the species listed.
CO2 mostly, but also KH, most of the species tend to like lower KH's.
I've ruled out high ferts as a possible cause(EI), sediment, 100% ruled out(ADA AS) and light(plenty of that via a light PAR meter), filtration(high grade current and wet/dry filtration, high O2 levels), good current, good general care.
This leave smostly KH and CO2.
The KH where I live is excellent but does vary, from about 15-20ppm to maybe mid to high 30'sppm.
This is very good soft low KH water.
So that leaves mostly just one parameter.
Lower temps= easier to get non limiting CO2.
Less light= easier to get non limiting CO2.
Wet/dry filter(set up right)= easier to get non limiting CO2.
Good care, observations and water changes etc etc.
What are the odds that all 400 or so plant species all have the same non limiting ppm of CO2?
Do you think that UG and Downoi are the same as far as CO2 as say Hygrohila difformis? One might need 50 ppm for a given high light value, whereas the other may be only 15 ppm.
One of the goals many have is to be able to grow any species. But even there, scaping with them is still another level of horticulture that is increasing difficult. Many can farm and grow, but cannot scape effectively with many species.
I would suggest trying both.
They can both lead to the same goal(more plants, and also nice looking scape).