It’s certainly true that “customer” is a loaded concept in “our civilisation”; and to say that all sorts of individual manifestations of that culture would not exist if that culture were not as it is, is true but (it seems to me) trivial. I don’t know if there’s any evidence for the origin of civilisation in commerce either, but it seems to me unlikely on the face of it that the modern concept of customer would have persisted relatively unchanged over such long periods of history as you seem to be suggesting. A fascinating analysis of the changing meaning of key cultural terms over long periods of history, which is grounded on linguistic analysis, is Emile Benveniste’s La Vocabulaire des Institutions Indo-Europeennes. I thought it was wonderful, and recommend it to you heartily.
Leaving that aside, however: it seems to me that there’s a sense in which people like me who use your products aren’t customers, and that’s because of the amount of effort we’ve invested in being able to use them. The process of becoming able to use a product like Excel seems to me a lot more like learning a language than buying a thing, both in the sense that it takes time and effort to become proficient in expressing yourself, and in the sense that the Excel I learn is different from the Excel you learn, based on our previous experience and the context in which we want to use it. But, for both of us, having learned a particular language (my Excel, your Excel) makes the cost of change relatively high. Even small differences in other spreadsheet products feel like bugs to me (until I get used to them…)
It seems to me that one of the key points about treating people like customers is making it easy for them to switch between products of the same kind. TBH, I could do a lot of my Excel work using 1–2–3 V1a; but the cost of switching (back) would be high because I’m used to expressing myself in Excel. If there were different products which all worked the same as Excel for the things I want to do, then I might be a customer and switch based on reliability or price or all those customer-type decisions; but there aren’t — at least, not in my experience. So I kind of think that you shouldn’t really be treating me like a customer: you should be treating yourself as a member of the community of Excel speakers, if that makes sense.