Water adjustment is really common do to in beer brewing because we've learned the importance of proper pH during mashing/boil (acid-base), proper minerals for yeast health (calcium, potassium, magnesium, etc), and appropriate mineral levels for flavor (sulfate, chloride, sodium, magnesium, etc).
I build a different water profile for every beer, based on the beer style and pH requirements for the particular grain -- in accordance with best practice.
Common practice doesn't equate to best practice. It's interesting that winemakers (mazers in particular) are lagging so far behind what's generally considered best practice in the brewing world. Water minerals definitely play a large role in flavor both directly and by affecting yeast health to reduce off-flavors from fermentation. So in my opinion it's not great to ignore that aspect -- especially in mead, where it's mostly added water.
This is why Bray uses a particular brand of water and adds a buffer. I don't know whether it's "optimal" but it clearly works for the yeast he uses.
There's such little information about adjusting water in mead I'd think I'd have to do a bunch of research before even beginning to try to design a generic optimized water profile. What minerals does honey contribute? How much does it vary? What are minimum levels of minerals for yeast health? What pH target and amount of buffering works best for the must? Should it be adjusted during fermentation?