No, I already suspect that and I'm not the sort of person that's going to waste my time or anybody else's by seeking validation.
You can spend a long time trying to prove a negative. You'll spend less proving to yourself that proper water management does make a difference as many here have suggested you do.
I'm waiting for somebody to provide something as trivial as anecdotal evidence of the improvement in their beer moving from tap, to RO/DI, to treated RO/DI. By that I mean how did the appearance, smell, taste, etc improve? I'm not being style specific, either, any example will do.
Well, OK. The first time I got it just right it was a Vienna. As soon as I tasted the first glass I said to myself "This is the best beer I ever brewed." That is a fairly non specific statement and it is a bit hard to be specific. I call often call it the "Ah" factor because that's what the drinker says when he tastes it. As one fellow put it here and I have never been able to say it better "All the flavors become brighter". That's still pretty non specific. In this case the essentials elements were control of mash pH to an appropriate level which I implemented with sauermalz, reduction of total minerals to the lowest possible level consistent with a proper level of chloride and elimination of sulfate. The overall impression on the palate was soft but full bodied, the malt component was delicious and the hops present to the extent necessary to balance the malt sweetness but the bitterness was very fine (as a consequence of zeroing out the sulfate). The beer required less lagering i.e. it dropped clear, the jungbuket evanesced faster than usual and the head became the classic meringue.
The "All the flavors..." quote came from someone reporting back in his experience on following what I essentially set out above in his own brewery and as he did that on his own I guess we'd have to accept that as a second piece of anecdotal evidence. If you look back over the posts I think you will find many that imply that manipulation of their water has improved the beer. More and more professional brewers are moving to the RO route and becoming more sophisticated in their understanding of the interactions of grain, hops and water.
The world's most sophisticated brewing setups belong to the Three American Horses.
I have no idea what that means and a Google search does not help.
Sophistication in and of itself is never a reason to do anything and is often enough a reason to explicity avoid doing something.
I'm not sure you understand what sophisticated means. From the OED:
"(of a person or their thoughts, reactions, and understanding) aware of and able to interpret complex issues; subtle:"
Perhaps you are confusing sophistication with sophistry - same root.
I've been doing practical chemistry experiments since I was in the first grade, sometimes with or seeking to create extraordinarily dangerous chemicals. I really rather doubt that screwing around with cation levels in RO/DI water would pose much of a difficulty for me.
Brewing water chemistry is Henderson-Hasselbalch modified to include Debye-Hückel. Because of the non linearities solutions of even simple problems (what's the pH of a liter of water whose alkalinity is 100 after 2 mL if N acid have been added?) require an iterative approach. Beyond that if we are trying to match an ion profile by adding salts and dilution water we have a linear programming problem with all that implies. You might very well have a problem with some of that stuff if you haven't used it before. Put another way, it isn't the chemistry that's a killer here, it's the math that you need to get quantitative results. But you don't need to do any of that stuff to benefit from treating RO water to improve your beer. Other people have done that for you and we don't as I mentioned in the earlier post, chase profiles any more except in the broadest sense. You can follow the Primer which involves no calculations more complicated than figuring out that if the dose is 5 grams per 5 gallons then the amount to use for 7.5 gallons is 7.5 grams. There are multiple spreadsheets out there to do the work for you if you want to be more sophisticated than that (and most of them ignore the non linearities and ionic strength considerations and get answers that most consider adequately accurate).
You can't screw around with just cations.
I'm prepared to grant anything on this subject if somebody will provide the level of evidence I outlined above, which should be a trivial exercise for the more experienced brewers that are obsessive note keepers.
No one here is actually asking you to grant anything. You have come here and asked why there is so much emphasis on water chemistry. The question has been answered: because proper management of brewing water can improve your beer dramatically.
Assertions that modifying your water produce noticable results, "because I said so", don't really fly for me.
The horse has been led to the water. It is up to the horse to decide whether he wants to drink or not. It would be a simple enough matter for you to brew a batch with modified RO and see for yourself. Depending on the style and the sophistication of your palate it might make a difference that you can detect and it might not.
I took good for brewing to mean that the measured PPM for the four cations did not provide for the possibility of an objectionable brew.
It is actually anions that lead to most of the problems, the main one being bicarbonate which is responsible for the dreaded alkalinity. Excess sulfate will ruin any beer, insufficient sulfate will lead to an insipid ale and any sulfate will destroy a beer that uses noble hops. Low chloride leads to flat, dry beer and high chloride to a pasty taste. Some beers want very little calcium, some want quite a bit but it is pretty flavorless. That's why you can't say a water is good for brewing without saying what it is you want to brew. I guess you could say that RO water is good for brewing because you can easily put anything it needs into it and, by extension, those people in the Pacific North West fortuate enough to have essentially RO water coming out of their taps have water that is good for brewing.