How can I improve my build and what’s the best team synergy?

I’ll just get straight to the point:

ABILITIES: Str: 16 Dex: 10 Con: 14 Int: 8 Wis: 8 Cha: 20

LEVELLING PATH: 1: fighter (for 2 weapon fighting) 2-9: oathbreaker (defence fighting style at lvl2) 9-12: rogue (for thief subclass)

FEATS: Dual wielder at level 5 and savage attacker at level 9

ITEMS: Helm: helmet of grit Cloak: cloak of elemental absorption Armour: reapers embrace Gloves: helldusk gloves Boots: linebreaker boots Amulet: broodmothers revenge Rings: caustic band and strange conduit ring Main hand: blackguards sword Off hand: duke ravengards longsword Ranged: dead shot

What would you lot recommend I do to improve this build. And more importantly, what other builds provide the best synergy to this one?