Re: Storm Needler and HE vs kinetc, etc - some good thoughts here! Is it fair to compare Railgun + Heavy Mortar vs HAC + LAG, though? A more fair comparison would be Dual LAC + Heavy Mortar, I think, and that becomes much less clear-cut. I don't think it's so much about per-shot damage - maybe it's more about the extra range on the higher-quality small kinetics.
But then HE in general doesn't have many "premium" options like the Railgun/Needler. The old Heavy Mauler for example could combine nicely with large kinetics, and iirc it was often the go-to for many loadouts. But HE that's "too good" is more problematic than kinetics that are too good... so in that sense comparing the best-available options for each type does make sense, even if it's not an apples-to-apples comparison.
Regarding ships that *could* make good use of large kinetics, per the idea of combining them with missiles - the Legion seems like a solid candidate, because it both has a bunch of missile slots, *and* fighters which can also benefit from kinetic support. And burn drive, which can potentially let it make use of shorter-ranged weapons...
I would use medium HE to combo with Railgun because 700 range is better than LAG's 600. Also, HAC has 800 range while LAG is 600 (but there is nothing better than Heavy Mortar, so 700 range is all we have for basic HE). That effectively reduces attack range to 600. (AI may try to armor tank kinetics is they are the only thing threatening it.) I rather take 700 range (from Railgun and Mortar combo) for general-purpose attacking. As for light autocannon plus HE, I do not know.
Heavy Mauler used to combine well with medium kinetics, but the slow firing rate and low DPS is such that I rather not use it unless it is the only option. Also, it is better if max range is kinetics instead of HE, if they cannot be equal, for AI's sake.
As for Legion, if I want it to be a good carrier, then I take Deck Crew and fighters, then I outfit it like a gunship. Legion had bad flux stats. I put two guns in the heavy mount and two dual flak on two of the composites. If the heavies were filled with two Hellbore, then one or two heavy needlers in more composites. If I use Mark Ix+HAG or Mjolnir+Heavy Needler in the heavies, then no more weapons. (All smalls are empty.) Rest goes into flux and hullmods. Legion is a carrier (and a gunship), it does not need missiles because fighters are better missiles than missiles (at least medium-sized missiles). If I want to play with medium missiles, better to use Onslaught instead of Legion. Legion is one of those ships where I leave most mounts empty to focus on fighters, but two heavy weapons with ITU plus fighters is enough to do serious damage to many things, which makes it a viable gunship, unlike other dedicated carriers.
As for Legion14, until we get the Champion, the point of using it is it is the only good platform for Hammer Barrage. If I want a ship to play silly and go nuts with dumb-fire large missiles, Legion14 is the only good choice.