> t's trivial and cheap to make water harder, home brewers do it all the time to replicate specific styles

I'm aware of this. I did it for my ribbon-winning brews. It is cheap at the home brewer scale, but at commercial scales, maybe not so much.

> can be shipped

Sure, it's possible to get genuine Saaz hops shipped from the Czech Republic to California. Again, A home brewer might be willing to shell out top dollar for a few ounces, but cost and availability is going to be a much larger factor. I've know craft brewers to abandon making certain styles because of uncertain supplies of key hops, and being unwilling or unable to switch to a similar variety.

There's a reason why so many the American West Coast IPA became a style defined by Centennial, Cascade, Mosaic, Amarillo, Chinook, Simcoe, Strata or Citra, and not like English IPAs and their Target, First Gold, English Goldings and Fuggles

The popularity of American hops in American craft beers is in large part because Ken Grossman wanted to use American hops and wanted to set himself apart from European-style hops. To my knowledge that's pretty different from terroir as it's typically meant, and also Sierra Nevada is pretty far from where Cascade was grown when they started buying it.

By the time you get to Stone or Lagunitas and their West Coast IPAs, the hops are being packaged as I described and again we're not really dealing with terroir. The Chicago Lagunitas products tastes identical to the California ones.

Adjusting the water for different styles or consistency across production facilities is a thing that is done at commercial scale. I had a professor in college who figured out how to do that for Bass' UK production facilities in the 1980s.

Sure, within limits. I don't think anyone is going to be brewing a traditional pilsner in Ireland, though. At least not profitably.