Got to admit I had to fast forward parts, but I don’t see how massive changes in the water you use is coffee’s fault?
Coffee is really predictably consistent, a human throwing it a curved ball is going to cause more inconsistency.
Whilst I say coffee is consistent, I mean that some of the things we measure are very consistent, some quite consistent, other factors have a wide deviation, but seemingly little effect on consistency, so it’s a case of focusing on the things that matter.
The order goes something like this (at dialled in grind):
Dose - you can make this exactly the same every time.
Shot/brew weight, small deviation but bigger than dose.
Extraction in terms of mechanical measurement is next.
Taste preference deviation is larger than extraction.
Total brew time.
Changing the coffee has the biggest influence on flavour.
Changing water for extremes, I don’t know why you would do this, but you can tweak to effect acidity.
I recall a paper a few years back that said high bicarbonate/alkalinity water enhanced crema (I guess CO2).