For the three people still playing DoT in 2025, here’s my recommended vertical investment order after some testing:

S1 Hysilens > E1 Hysilens > E1 Kafka = E1 BS = Jiaoqiu LC (for Swan) > E2 Hysilens

E1 Hysilens gets a bump since it's a unique multiplier outside the normal damage formula.
E2 is just meh. Why give a support skill as E2 to your main DPS?

Worst case, I could see them "nerfing" her by swapping E1 and E2 just to bait sunk-cost DoT fags