I don't nerd out with a microscope and study my bennies - but I know for a fact they do just fine in a hydroponic setup being fed synthetics.
I did a lot of nutrient experiments last year in an effort to cut costs and/or simplify things. I generally run a synthetic base nutrient, along with silica, kelp, and fulvic. I tried a couple things last year. Twice, I attempted a sterile rez - once using H2O2 and another time using chlorine. Both methods kept the root mass fairly healthy, but the plants were definitely not my best work ever in terms of both quality and final weight.
The other experiment I tried was running my usual nutrient recipe, but not adding bennies. Did this twice and both times i got pythium really bad. When I run the exact same nutrient recipe with bennies, i get beautiful, giant, white root masses. With the synthetic nutes I use as a base, this shouldn't happen if the salts were killing the bennies. If the synthetics are killing the microbuial life like you're claiming, then I should get the same results whether I use bennies or not. But I don't.