Absolutely right, we are on the same page, i just didn't make so clear as you did,Any acid depends on concentration AFTER dilution in the system. The concentration used does not matter but should be diluted before adding of over 5-10% to prevent burning the roots before it had a chance to fully dilute.
Citric acid is a very bad choice for hydroponics because of its chemical reaction with bicarbonate to produce co2. This makes it very poor for stability.
Any acid will lower PH some are more stable than others. It's not the type of acids that makes them damaging its the PH they created that burn you. Hydrochloric acid sounds dangerous and ppl think oh it's worse for plants and microbes but that's false... its all dependent in the concentration of any acid.
To add you don't know how much it drops the PH there is absolutely no way to calculate this without knowing the alkalinity of the water.... 1 drop of 5% Citric acid in a gal of RO will drop it drastically. In an alkaline water like very hard well water it won't do anything
I personally use phosphoric food grade 86%, but of course the EC value makes huge difference how much need to be adding, my water are RO and i never add drops in, first dilute and wait 10 min, after slowly adding.
What i want to say in my previous post, i absolutely do not recommend to use pure acids in hydro for beginners.