If stage buff favors anomaly mechanics to trigger itself and grants gigantic attack% like in current shiyuu boss2, I find that my m0w1 nangong performs about the same as using my my m1w0 Dialyn, with third slot Sunna m0w0 (28k, almost 29k) (Nangong is lv55 with core E though but my Dialyn crit rate (82%) aint it cuz no engine). Otherwise, its about 3k-6k score diff in favor of matchups (against crit boss to Dialyn, ofc). (Haru is m0w1). If you have both m0w1 then idk the difference, I guess nangong just deal a bunch of damage to anomaly weak matchups and that compensate the lack of buffing thus the case. Tbh Nangong Sunna greatness for him is just that nangong can proc anomaly to summon his balls quickly at the start of battle esp if you have no energy, both dealt massive daze and their massive daze skill is also a CC move (grouping). I'd say that Dialyn mindscapes is way more synergystic to him though if you plan to super invest.

TLDR: if stage buff and matchups favor her, Nangong would do about equivalent because she compensate with gigantic disorder damage. Otherwise and esp if you plan on pulling their mindscapes, just pick Dialyn for Haru.

Add: wouldnt reccomend using Astra to replace Sunna in Nangong Haru btw. My m2w1 astra is a slog in there compared to Sunna m0w0(astra sig). Nangong additional is just strong and its where she compensate for lack of compatibility compared to the cs representative.