Have you tried triple ion pulser Harbinger with smod expanded mags and phase anchor this release? Absolutely belts out damage. Gorgons are also good for them or swarmers for killing fighters.
Optimal Afflictor bypasses shields (any shields, omni with accelerated shield hullmod included, and AI doesn't keep 360 shields up consistently enough for that to be a counter) with 4AM blasters while target is under it's system's debuff (+50% damage, so effectively 6AM shots). This almost one-shots skills-less sim capitals. Officer-ed capitals take 2-3 passes. Cruisers 1-2 passes.
Doom can't bypass shields via mobility, but it can force enemy to rotate shield out of the way via mines or partially bypass shields with mines alone (drop mines in sync on opposite sides of enemy ship, at least one side will be unavoidable, unless enemy can run away). It also has a lot more flux to directly dump into enemies via time dilation to dissipate/reload faster (+anchor).
Current Harbinger doesn't excel at anything. It's too slow to outmaneuver shields, current Quantum disruptor is just a single use system with long cooldown. At most you'd be able to shoot 3AM blasters in this time window (medium slots aren't an improvement in single shot power, AM is still better). Harbinger has somewhat more flux than Afflictor, but can't use it anywhere as effectively.
Afflictor and Doom are capital-grade threats when player-piloted. Harbinger is not.