Looks like you have a too narrow definition of combat builds then. You see, just like explorer builds, combat builds have subsets too. For exploration, you can go for higher jump range ("space" exploration), and you can go for planetary builds. (And fuel rescue, and hybrid, and so on.) If you specialize for jump range, your ship will at best be decent for planetary exploration. If you specialize for planetary exploration (cockpit visibility, forward speed) your ship will at best be decent for jump ranges.
As for combat, you can at the most broad level build for PvE or PvP. (Not going to go into more specialized subsets now, as they aren't relevant to the point, but I am aware of them.) Sure, you can take a PvE ship into combat against players, in the sense that you can take anything into combat, but a PvP build would be best. A PvP build will do okay in PvE combat, but won't be the best there either.
However, since we were talking about the Thargoids here, I have to admit that the thought of PvP there didn't even cross my mind. Bringing that in would just be moving the goalposts.
About turrets, they also have their niche: fighting off multiple small and fast targets. They are almost entirely worthless in PvP (although have you faced a wing of iEagles armed with medium beam turrets and missiles?), but as it so happens, it would be the exact niche for fending off Thargons. When I was comparing the Anaconda and the Cutter, I mentioned that the latter has better turret coverage.
Also, did you really mean to say that neither of those two ships are not intended for multicrew? I'm fairly certain you didn't.
Bit more about the Thargoids:
Back in the original Elite games, if you encountered Thargoids, they were hostile. It was only in FFE that they didn't shoot at you first. I'm a bit unclear about how much from that game is considered to be canon when it comes to the aliens though, but there was one other part from it relevant to what you wrote: when you had the option of getting a Thargoid ship of your own (completely OP, of course), then they said that they'll have to extensively modify an existing ship so that you could use it. I guess because the silly humans only have two arms and pump their air full of that horrid oxygen instead of nice proper ammonia.