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

So E0S1 Hysilen would give
>50% vulnerability (20% generic + 30% DoT)
>25% def shred
>10% party speed buff
>8 instances of additional damage every time enemy takes DoT damage (Kafka can trigger 4 times per turn)

Having to roll S1 sucks, but isn't that pretty good on paper?
For comparison E0S1 Cipher gives 40% vul + 24% def shred.
And Hysilen has 6 different debuffs so you can probably put her in Ack team