I definitely think having an SLF helps
SLFs, used properly, are a huge asset to any ship that can carry them.
Seems to be a bug currently that can cause performance issues with other peers though, especially if commands are issued too rapidly...so it's important to avoid that.
About week ago i made some tests with Morbad, he tried hull-tank FAS with different layers of defences vs seekers against my Plasma/seekers Cobra, he even uploaded video on youtube from 3rd(last) test, In all fights he had LR legacy PA's with TLB, AFMU and at least 1mrp(IIRC 2 but not sure) and HS(s)
In first he had single PD, he lost weapons with large chunk of hull with me sitting comfortably at over 70% hull, 2nd fight when he tried to use frag instead of PD lasted maybe 2 minutes with him losing all weapons, in 3rd with 2 PD he secured win.(cancelled my synth 3 times and i lost canopy at about 30% integrity left, so I would say lucky) And it was mid range TLB on relatively nimble ship against IMO not greatest small PvP ship. At the end we agreed that vs single hounds he had no play at all, BUT it was FAS. gunship have much better utilities placement for dual PD.
Was two MRPs, which I'd probably consider the optimal number on the heavier medium hull-focused ships.
Single packhound, with their lower velocity, might have been counterable with the dual PDT setup, especially with more careful range control, but the FAS is really not good against missiles. It's acceleration, especially with regards to laterals, is mediocre (a big deal for giving PDTs time to engage) and it's utilities are poorly placed.
Gunship has even worse practical acceleration, but at least it has better utility placement, as you note. Having a PDT equipped SLF around can be handy as well.
it's just power of skill boosters that make opportunity cost of taking PD's or chaff too high
Yep, this is the crux of the issue.
There is essentially no combat situation where more shielding isn't of some use, with the possible exception of having your shield gen knocked out early on without the ability to get it running again. Every other utility is more specialized, especially since they all have very common counters to major functions. Heatsinks can't counter emissive; chaff does nothing to PAs or rails; PDTs are really only useful against modest numbers of munitions and, excepting flechettes, are only really needed once shields fail; ECMs are mostly garbage against anything that's not a hatchbreaker, unless you stack them to absurd levels...and the rest are just dead weight when it comes to actually fighting anything.