I firmly believe she would have kept firing until the ship melted to slag.
Yes, she would. For anything else than a players ship it doesn't matter. You must be a terribly bad shot that an NPC would self-destruct by heat before you shoot it down. Once the NPC is destroyed, the next ship again comes with everything at 100%. Only on a players ship, surviving for much longer, it matters.
I get why they did that though. They did not want interceptors getting instantly face rolled by just one or two big 3 ships loaded with guardian shard cannons.
Yea. I actually find some strange appeal in the four-slot limitation. It actually makes more things useful for AX duty. Without this limitation, the number of ships actually useful for this task would be much smaller.
In the end Thargoids are balanced around the best setups you can bring against them. If you can bring more firepower against them, they have to be more sturdy to still work. Which means that other ships without less firepower will be of lower value.
So yes, the four weapon limit seems very random. But it does have some use and actually in a strange way adds to the game. There might've been more elegant ways to get to the same goal, but this is the path FD has chosen. Considering how unlikely a complete rework is, I guess the current implementation is here to stay.
Edit: and as I haven't commented on one thing on the thread yet: small seismic launchers. I am all for those. It would give the ability of core mining to some ships, which would seem like a logical choice for that activity, would they just be able to have a seismic launcher. Also, the model of the seismic launcher might even already be small enough to fit on a small hardpoint. (It looks a bit lost on a medium one, for sure. )
So really, copy the thing and just reduce the ammo on the C1 version and it might already be good to go. I can't see anything wrong about that.