Sparks are currently overtuned yeah. Major factors:
1) High wing size + shield = surprisingly durable. 2250 effective points of health, except that its shield only takes .25 damage from frag or .5 from HE! So more vs many common PD weapons (can the shield dissipate soft flux, or are fighters weird/special? If it can, then beam based PD has a built in 50 dps damage reduction). Thats the same effective health as a Broadsword wing, though the broadsword has much higher armor.
2) Exceptionally accurate and long ranged: perfect accuracy at 500 range is a greater effective range than other interceptors or fighters. Heck, if a Talon or other gun based fighter is more than like 200 units away then its bullets are going to miss. Sparks have a longer effective range than many point defense systems, though they will also fly closer than their max (attack run range 200 according to wiki? Dunno if still accurate)
3) Damage downside goes away when massed. Soft flux doesn't matter if you have enough of it. Burst PD is front loaded with multiple charges, then the per wing DPS is 320. BUT: whenever the Spark overshoots the target and is out of firing range, it is still recovering charges! So when it comes around for the next pass, it has another burst of higher damage.
4) High armor penetration for a fighter (not sure how long the duration is, but its 128 damage and I think less than a second, so probably higher than 64 effective penetration). MUCH higher than kinetic or frag based fighters, and still a good deal higher than IR pulses.
5) Very high speed.
Honestly the biggest issue is probably armor penetration: the little buggers are way too good against heavy ships.