Don't know. Do Fullers do clones?
I'd guess Big Brewers stick with their water and own it. Maybe adjust the grain rather than water just for cost and ease. Surely when you brew on that kind of scale you can afford to?
I just want to brew 'all-the-things' and less than 5g of CaCl2, MgSO4, CaSO4 and Latic Acid is good enough for me.
But, at the end of the day, I'm brewing for myself. I like my beer and that's how I roll.
If I was trying to sell it I'd be fucked. 🤣