Is the Subterfuge tree even that great? Maybe poison + lightning flask, toxic cloud / caltrops + upgraded flask of fire, toxic cloud + flask of ice. Flask of ice is actually better than its description, it freezes enemies before they hit you and seems to work even when you're flanking them and they look like they're attacking your tank (or maybe that's just for aoe attacks?).
I tried making Sera a Subterfuge archer tempest before I realized that toxic cloud isn't a grenade, it starts where she's standing and slowly drifts towards the targeted enemy. So maybe DW would be better for that. Still, toxic cloud does so little damage and has such a brief duration it almost seems like the devs said "well rogues aren't supposed to have AoE attacks so let's make it extremely weak."