TLDW;
In the first part, I tried to compare them with Melt Burst (Hu Tao’s burst on a Melt reaction)
Test 1:
Kazuha 940 EM -> Burst Damage 298,751
Test 2: Sucrose 880 EM -> Burst Damage 295,287
Kazuha’s EM is naturally higher because of his ascension stat bonus, so in Test 3, I tried to adjust kazuha’s EM equal to Sucrose’s EM
Test 3: Kazuha 880 EM -> Burst Damage 295,247
In the second part, I tried to compare them using Overload (actual crit damage + overload damage)
Test 1:
Kazuha 940 EM
Crit E dmg 18,430 + Overload 10,519 = 28,949
Test 2:
Sucrose 880 EM
Crit E dmg 15,426 + Overload 15,387 = 30,813
In summary, both Sucrose and Kazuha’s buff just provides almost the same damage boost on Melt/Vaporize reactions on an equal Elemental Mastery point, then Sucrose’s buff provides a greater boost for reaction comps like Overload, Electro Charged, Swirl teams.
So in the end, Kazuha and Sucrose have different purposes on a team comp.This changes of course on a C2 Kazuha where he gives the whole party an instant 200 EM buff and on C6 Sucrose where the whole party gets a 20% Elemental damage bonus on the absorbed element.