Most of my Banshee builds run with a very large engine to be speedy for an assault. With the lower max engine size, the 3S can take greater advantage of many hard points. For long range sniping, there is a Gaus rifle that can still be used in short range with little heat buildup, and an LRM20+A. There is enough ammo for each to keep a steady barrage of fire for a good while as you chug along to close the distance for your medium lasers. The small lasers are there for a bit more oomf against those pesky lights that will be circling you, and prevents ghost heat from adding another medium laser. This build also can zombie fairly well.
Drip the small laser, they are not worth it. Either swap them for a single medium (forget about the arm) or get a tag. That having said, you REALLY need more missiles for a LRM20+A. If you plan on investing less ammo like that I would suggest getting instead an LRM15 without +A, you can get ammo along with something else with that tonnage, and it gives you more shots. Those 2 ton ammo LRM20 are only good for lore as in storybook. Trying to run one in the battlefield is bad, and running a sub-par mech means you are a liability to your team.
Took some of your suggestions and changed it up a little. Downgraded to an LRM 15 and dropped the small lasers, in exchange for more ammo (total 3 tons of LRM and 4 tons gaus), a seventh medium laser, and tag. I love a STD engine in the 3S, as it is a pretty effective zombie, so I tried to use all the slots. It still doesn't feel quite right with the odd 7th medium laser adding ghost heat, but I'm not sure what I could change besides downgrading medium lasers smalls to add a large laser or PPC or something. I am not satisfied with a build unless it uses all slots
This variant drops the LRM for a Narc, which I've always absolutely loved when other people bring it but never actually fielded it myself -- I haven't tested it out much yet, but it kind of makes sense on a brawler zombie build because you'll be on the front lines anyways. It also moves back to 6 medium lasers (no ghost heat yay). This saved enough tonnage to mount an ER PPC for some more consistent long range fighting. The flamer is there because I hope it acts like a machine gun and registers a lot of hits for lucky critical hits, they look cool, and it is super annoying to enemies when it blocks their vision. Obviously, the ER PPC isn't used when the mediums are in range due to heat concerns and it runs at 41% heat efficiency without it, and there is no appreciable heat buildup outside of medium laser range.
