Can a serum brighten dull skin without exfoliating harder?
Yes, if it hydrates and exfoliates in the same step rather than doing one at the expense of the other. That is the whole design of the Anfisa ÂN-DEW, and for dullness the order of importance is different from how most people read the label.
Gluconolactone matters most here. It is a polyhydroxy acid with a molecule large enough that it works slowly, and it holds water while it does. You get a smoother surface and a more hydrated one at once, which is exactly what a flat complexion is short of.
Hexylresorcinol evens tone by acting on tyrosinase. Dullness and unevenness usually travel together, and a patchy tone reads as tired even when the texture is fine.
Azelaic acid takes down the low-grade redness underneath. Most complexions described as dull have some diffuse pink in them, and calming that changes the overall clarity more than people expect.
Behind those: glycerin and jojoba for water and lipids, licorice root and kakadu plum for antioxidant support, green tea and ferulic acid.
An AHA would resurface faster. On skin that is already tired, faster is not the same as better.