The sources I found state honey has a low end pH of 3.0-3.4 and a high end of 6.1, with an average of 3.9.Many, if not most of the mead makers I am acquainted with will front load acids and tannins. I prefer to wait a while after stabilizing for my acids so the bulk of the yeast and particulates can fall out and I can balance to taste more accurately. I never make assumptions about how much of anything a new honey varietal will need, and wait until aging to consider adjuncts of any kind.
While yeast is happy with pH in the range of 2.9 to 6+, spoilage organism like less acidic environments, so a pH below 4 is generally recommended (some folks want lower) to prevent a large percentage of spoilage organisms from thriving.
To avoid problems, it makes sense to ensure the pH of the must is 3.9 or lower. On average, a slight reduction of pH is warranted.
IME, mead is bland and insipid. Adding lemon juice and zest prior to fermentation lowers the pH and gives it a flavor boost. YMMV
I don't normally make large acid additions prior to fermentation of any wine, if the must is in the 3.1 to 3.9 range. I adjust by taste prior to bottling.