When using humnic and fulvic acids in hydro the difference is enormous. Even i sometimes think wow that almost tastes organic. But no I dont mix up my own, thoiught i dont see why one couldnt use his own humic and fulvic concentrate. I find in hydro youre better off keeping it simple and sticking to bloom food, vitamins, carbs, bloom enhancer (Big Bud does the job quite well, no PK 13/14 or any of that, it kills the taste completely) and if you have the patience humic and fulvic. Beware of root rot when using fulvic and humic. Also bombarding plants until buds are half an inche wide with an organic cocktail or teas really improves the taste and smell, just be sure to keep reservoir ppm low.
In respects to most nutrients i think you might be wrong saying that most hydroponic nutrients are chelated from leonardite, but i cannot provide background. And even if they are chelated from leonardite they wont be the same as using the fulvic and humic acids concentrates.
If youre doing organics the way it should be done with a well ammended soil, you should try your hardest to increase microbial and bacterial activities in the soil, since those are what actually make the organic nutrients available for uptake. Since humic and fulvic sort of do that, its an extra helping hand. Plus compost teas really are the shit and i also add 1 worm per gallon of soil in pots at beggining of flowering.