I think you have a good case of 'confusing yourself with the facts'...There are many opinions in the context of what you just posted. Even books written on each facet. I think that soft water and stable TDS is why my fish thrive, but that's my opinion. When I come home from out of town, my fish seem happy. But from the difference in the amts of water I change vs. my wife, the ph differences are scary...fish are usually fine either way, as long as the TDS remains the same, or close...that's my take
FWIW, Jim, Mark, and I all have slightly differing views or approachs on RO, so perhaps there's a case of 'too many cooks'...dunno, matey...