Deathmark is an Auto Attack set with focused on Weapon Pool Skills, Beronath isn’t the great AA but extra RR you have compensated that loss. So you should focus on that and Ring of Steel without proper investment(I mean modifiers) and with Dual Wield(it only uses your main hand weapon) isn’t that good. But if you wanna focus on that you might need a gear change though infiltrator won’t be the best class combo.
Check my Deathmark Dervish. Infiltrator certainly have more active skill to use.
And check this DM Inf though it’s a bit outdated but you get some ideas. You should focus what you can do best. RoS is just side damage without modifiers. It’s fumble is useful againts certain enemies though.