LAG versus Light Mortar: which is better depends on what you're using that weapon slot for.
For a ship looking for anti-fighter weaponry, the LAG is vastly superior. (For anti-frigate, the LAG is probably better, though it's a much closer competition.)
For anything that's tight on ordnance points and flux dissipation, but has small ballistic slots to spare, the light mortar will be the better choice.
For a frigate or destroyer that's expected to be going up against destroyers or cruisers, the light mortar will be the better choice.
Remember, when looking at weapons for cracking enemy armor, raw DPS is much less important than per-hit damage. (Though raw DPS is not completely without value, as proved by the assault chaingun.)
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For officers, I'd suggest something close to this:
https://fpdk.github.io/?s=0303102330435363738090x10001020304050607080x23031020304050x30001020304050Note that officer personality is important here; you want aggressive. (Or
possibly reckless, though if you do go for that it's usually a good idea to leash the ship by setting it to escort something with a steady officer...)
You want Combat Endurance for sure - extra peak time is very important for SO builds (and frigates and sometimes destroyers), and the level 3 perk is an extra 5% to several useful stats (if you go into the fight with max CR - which you should be doing at least most of the time.)
Evasive Action and Helmsmanship are easy skips - the benefits to ship mobility from the skills are relatively small compared to the benefits from just having SO and the zero flux speed boost all the time.
Gunnery Implants is good - the extra range matters even for SO ships. Similarly, you will want ITU/DTC on any SO cruisers you put together. (And, as an added bonus, having Gunnery Implants means they'll still be worth using on a non-SO ship later on if you change your fleet composition.)
And after that I go for all the defensive traits; they synergize nicely and help keep the idiot aggressive AI alive.
Of particular note here is Advanced Countermeasures. Take this one to level three! Fighters are the bane of SO or phase ships, keeping you stuck in combat when you're trying to back off and vent. They'll be much less of a threat when you're doing 50% more damage to them, though.
...And that leaves room for only one actual offensive skill; I prefer Ordnance Expertise for its bonus shot speed perk. (The extra durability on your own weapons is good, too, especially for armor-tank type ships.)
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For ships, I'd suggest looking into an SO Dominator; dual Devastator cannons with flak and railguns works quite well. (The Devastator isn't normally a good primary weapon due to some shots detonating early - but with SO clamping your range down, it basically turns into an explosive shotgun.)
