I have to agree with Dreamdancer on the Nibelung... though, interestingly, the unique version with the built-in large cannons does still have converging forward mediums, and the build I've ended up using with it is actually broadside-friendly. 2x heavy needler, mixed GH PD weapons in the small turrets, small side mounts left empty for more ordnance points. It actually works out pretty well: you approach head-on, get some burst kinetic damage in from the pair of needlers, then swing broadside to get all three heavy guns on target once the target's running high on flux.
I'd say the issue is a two-parter: one being that filling those small side slots doesn't get you a lot of advantage, since it's easy to have just the large and mediums alone occupy the entirety of the ship's dissipation. And two being that filling them with anything more than light mortars gets expensive; a full set of railguns is running you 56 ordnance points, and even if you plan to focus on broadside combat, it's better to spend those points elsewhere.
(Plus, using light mortars isn't actually that useful - if the side guns had wider arcs they might serve as decent anti-fighter weaponry, but with the narrow hardpoint-style side mounts, you're pretty much locked down to fitting them with kinetics - light HE weaponry isn't very effective against large targets and they don't have the traversal to be really useful against small targets. Though a version that allowed ballistic or energy weapons for those slots might be interesting - imagine swinging to the side to bring in a battery of antimatter blasters, or filling the slots with range-boosted ion cannons for a support role...)
My suggestion would be to remove the Heavy Ballistic Integration hullmod; unlike the Conquest, the ship doesn't need a bonus incentive for actually using large weapons in its large slots. Instead, I'd suggest something like a "Integrated Light Weapon Batteries" - something like -5 OP cost for small ballistic weapons, +5 OP cost for PD weapons. (And then maybe restore the medium turret arcs to what they were?) The idea is to reduce the opportunity cost of filling those side mounts, without making it vastly cheaper to fill out the small turrets with PD guns. An arguably-beneficial side-effect would be making larger PD guns more expensive, increasing the cost of doing silly things like tossing a single flak cannon into the rear large turret and calling it a day.
