I'm almost certainly over thinking this as we have lived with very hard water for decades. Our plumber advised os to tip a teacupful of white vinegar around the stem of our kitchen mixer tap, and I use citric acid to descale the kettle, using the water from that to do the same for the shower head.
Hardness of water varies dramatically, even within the same supply area.
Much of the UK has hard water, sometimes exceptionally/aggressively so. Here in Surrey, all three of my previous addresses supposedly had hard water, yet none was nearly so bad as the house I ve been in since the late 90s.
All had the same water company (SES) and are within about 10 miles from here, so clearly some localised issues. The other addresses were all fed from reservoirs fed by rivers, where as the current address is all from a deep borehole.
I wouldn't go back to unsoftened water here, because every drop of water that evaporated would leave powdery scale deposits that you could see and feel; and keeping on top of the scale was both hard work, and a form of chemical warfare.The deposits also built up in clothes and made soap scums on surfaces and inside of appliances. The old hot water cylinder had several inches of scale and sludge.
One of my first DIY tasks was to fit a water softener, and then to replace all the pipework,
The scale and scum issues are massively reduced,clothes feel better; all cleaning/washing is now easier, more effective, and quicker, using far less detergent and few chemicals. I can really feel the difference when someone (me) forgets to fill the softener!
I wouldn't do without a softener here, but I'd like to move somewhere I wouldn't need one.
It was having the blank canvas of a new kitchen install that got me pondering. With regard to teeth, I think it's the fluoride dosing that is responsible for that.
My water supplier don't add any fluoride as its already present naturally in the hard water.