Is "well water" (drill hole into water table, pump out water) always used raw and unfiltered? Has it traditionally always been safe to drink anywhere you can sink a well, or is there some history of bad wells due to natural contamination? ...
Usually used raw, even now. No it has not always been safe, but much better these days.
You have hit most of the points, but there is one thing. Before WWI wells were often down to the water table, like the stone wells with the bucket and crank handle. But more recently most water wells are much deeper, usually below a layer of rock, so that they are protected from surface contamination. I think the wells around here go down 500 to 1000 feet. (?)
Mineral content tasts bad and makes build-up on things, but is not usually harmful. See "Artesian Well". Bacteria, which can be harmful, is not usual that deep. And it can be harder to remove from the water, unless you boil it. I think Reverse Osmosis is to remove minerals, not bacteria. (But maybe both?)