Need pro help with getting more damage from volcanic fissure of snaking.

Ninja is telling me like 1.7 mill damage while a lot are 7 mill damage.
What an i doing wrong? i would prefer to stay with non crit build as quite a few on ninja are the same (?), almost the same and have way higher damage than me.
Loosing defense for me is a no/no cause i'm old and slow.
Any help appreciated, even if you tell me what i need to improve.
Thanks guys.
Build is Mercenary_Daryl.

Bump, anyone please?