That's not really a virtue, tho. For example, strength. Does a +3 on d20 roll really reflect the difference between a big, strong orc slamming into a door, and the small, frail elf? There are a lot of cases like that.
That’s more an argument that the bonus or die type used for the unified system isn’t a good fit than one that unified mechanics are bad.
For example, swap out the presumption of a d20 (flat-distribution) for 3d6 (bell distribution) and suddenly that +3 can make a significant difference on edge cases.
Similarly, if the small frail elf didn’t have a +0, but a -1 modifier and the big strong orc didn’t have a +3 but a +5 there will also be a significant difference in performance, particularly over the course of many rolls (sure, the big orc might whiff a door check now and then and the frail elf get lucky, but the next round the orc checks again and passes and the elf bounces off the next three stuck doors they come across).
So again; your argument is only relevant to one particular instance of unified mechanics, it does not function as a blanket dismissal of unified mechanics as inherently flawed by nature of being unified.
Case in point... WEG Star Wars vs. d20 Star Wars. Both use unified mechanics, but WEG’s are actually properly tailored to the setting and function gloriously in that purpose, while d20’s are not because trying to fit Star Wars style action into a 3e D&D framework just isn’t going to get any remotely close.