Sucrose (砂糖) is better than Kazuha. She is a better battery, gives EM without constellations, gives dmg bonus, can use TTDS. Her scalings are also quite high, so you can even build damage into her.
Sucrose can be used on taser teams, the kokomon team, any team where you would use Venti or Kazuha, including national, Childe international, melt, vaporize, etc. She is one of the best supports in game.
Two of her passives buff EM. One increases EM by 50 upon swirl (for 8s). Another increases EM by 20% of Sucrose's EM upon using Sucrose's E or Q (for 8s). This EM buff is absent in Kazuha's kit until C2.
If Sucrose has 1000 EM, she can give up to 250 EM to party members at C0. (Nahida can also give 250 EM with her Q. The difference is Nahida's effect can last longer. By contrast, Kazuha's C2 can only give 200 EM, which is quite sad given that is a C2 for an Anemo unit.)
Kazuha has a passive that gives dmg bonus based on his EM. Genshin has explained before in 1.6 that one cannot use Sucrose's EM buff to buff Kazuha's dmg bonus buff to avoid an infinite spiral. (The developers explain that otherwise, if they add an effect that gives EM based on one's dmg bonus, then the two effects can be stacked infinitely.)
C1 gives extra charge on E, good for battery. C2 extends duration of Q by 2s, which is ok. C4 is not needed. C6 (Chaotic Entropy) gives 20% dmg bonus for absorbed element in Q. This dmg bonus buff can match or surpass C0 Kazuha (depending on how Kazuha is built).
Build
For artifacts usually always use VV. There are times where you can use 4p gilded if using Sucrose as an EM bot. This is usually better for dendro teams as anemo and dendro do not react, which would make gilded better than vv in that case (example: 4p gilded, full em Sucrose as support for Alhaitham spread teams, alongside Nahida EM buff).
One can do full EM (for EM bot) or even build dmg ATK-anemo-crit since Sucrose's scaling is decent.
Very versatile, can be used on any team that needs Anemo VV (which is most teams). Some highlights include the taser team with sacrificial fragments.
She can even be used to buff dendro teams as she can give EM to the party. Because this EM buff, Sucrose can synergize with Cyno.