It is (or should be) obvious that in order to accurately determine the amount of acid we need to add to a brewing water to bring it to a desired mash pH we must know the acid/base properties of that water. In the waters that brewers use the acid base properties are those of the water itself and the carbonic acid derived species (bicarbonate, carbonate) dissolved in it. We need to know the total carbo (carbonic, bicarbonate, carbonate) per liter
and the pH. In the laboratory we measure alkalinity and use that to determine the total carbo. The alkalinity measurement is a titration and so the sample pH is determined during the alkalinity measurement. As it is needed to determine total carbo and, with that, do acid calculations, it is reported. The amount of acid required to establish a particular pH is given by the difference in charges on water molecules and carbo ions at the desired pH and at the original sample pH. These charges are a function of pH and thus pH is often referred to by water chemists as 'the master variable'. A robust spreadsheet will (and a couple do) require the input of the water's pH. The math is at
https://www.homebrewtalk.com/forum/threads/calculating-bicarbonate-and-carbonate.473408/.
If you take one of those robust spreadsheets, put in some alkalinity level and then calculate the amount of acid needed to reach some typical desired mash pH as a fraction of the alkalinity (remember that alkalinity is the amount of acid which must be added to a 1L sample to bring its pH to 4.5 (ISO protocol) though that number is, in North America, usually multiplied by 50) you would get a curve like this one:
Strong dependence on pH is clear as we approach the pK's of carbonic acid at 6.38 and 10.38. No surprise there. But few of us have brewing water sources with pH that high or low. In the more typical source water pH range the acid requirement is about 90% of the alkalinity. Thus if you have water that comes to you at pH 8.5 you with alkalinity 100 ppm you can quickly see that you are going to need about 0.9*(100/50) = 1.8 mEq of acid per liter of water to be acidified to a mash pH of around 5.5. Thus when someone says that water pH is not a factor it's clear he doesn't understand the chemistry and yet he is not that far off! In the typical range of waters we deal with the dependency on mash pH is a weak one. This fact allows spreadsheet authors to put out products that don't need to contain all the math mentioned in the Sticky linked above. While the math isn't that hairy and, to my way of thinking, anyway, one of the main reasons to use a spreadsheet is that hairy math can be hidden from, but still be available to the user.
Thus the popular spreadsheets do not do the full carbo calculation. You can be 100% certain of that if they do not ask for liquor pH. This is probably because of inertia as much as ignorance of how to do it. When most of these were written I'm guessing the creators did not understand the chemistry but at this point in time they probably do as it has certainly been discussed here and elsewhere extensively and the formulae are certainly online in several places (including the Sticky here). But to go back and rework a spreadsheet that is fairly complex because of the breadth of things it covers is not a trivial task.
A couple of other things should be pointed out. In a typical mash involving water with alkalinity of 1.5 mEq/L or so at pH 7 the water's proton deficit (acid reqirement) calculated as discussed here might be 20 or so mEq while the proton deficit of the malts might be 4 times that. Is, in such a case, a major rework of the water portion of a spreadsheet to render the water component of the acid requirement more accurate justified? To an accuracy freak like me, yes. To the 'better is the enemy of good enough' crowd, no. In this same regard most of the popular spreadsheets use primitive models of malt acid/base properties such that their predictions of mash pH can really only be used for guidance. The robust ones give much more accurate predictions if one has accurate malt data but one doesn't in general and so they really aren't that much better. Thus you could easily argue that errors from poor modeling of malts swamp errors from poor modeling of the water.
To sumarize: you are right. Any spreadsheet should ask you for the water's pH. But given the other limitations of them the fact that they don't really doesn't matter that much, especially if you water's pH falls between, say, 7 and 9.5. You can sail on with any of the spreadsheets you fancy, if you are in this pH range, confident that the error caused by failure to consider source water pH, is small relative to other errors.
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