Marksmanship is a nice option - make those centre line lances really sting.
I think - for a Bughouse swarm - that leaves you with three choices of second talent:
- marksmanship adds auto-criticals to the centre line gun. That's a nice-to-have but as you say will totally brutalize a tough large-base ship.
- intimidation feels like the best option as it works in various situations: if someone blocks you with a low initiative generic, you get easy kills on them, and it makes a dense swarm of bugs a nightmare for a high-agility, token dependant ace.
- treacherous doubles down on making your ship's tougher. A treacherous charge is basically a free evade, which is awesome, provided you're obscured by another ship. You can use your own ships (giving you further options to make it hard to finish targets off - tractor one ship in front of another and the ship at the back gets full agility, deflection AND treacherous, so is nigh on untouchable) but it's really, really good when facing swarms - when facing 5+ ship's they invariably come in in multiple ranks - treacherous means either the back rank is neutered or they'll have to spread out, which also gives you an advantage.