This is kind of my mind set too. At least with the Decayed, if we can team up with them, you would basically be dealing with just another group of people. Some are decent and some are assholes, but they have different factions so if the current leader is a problem you can work to replace him, and you can reason with them. But the Hive is just that, a hive of cannibalistic monsters, it's basically like teaming up with the mummies. And if they get strong enough, they will have zero reason to work with you and you can't just replace the leadership later with another person who is more amicable. Without meta gaming I don't see a single reason to go with the Hive. Neither in the moment we have to decide to leave Matis or not, nor after the fact when seeing how it shakes out after going back.
Also, for me, neither sex scene was really to my taste. The one at the mutant base left me with a bit of distaste for Fang but it wasn't the worst way I've seen a scene like that done and it was visually very good. The other with the Hive Queen was very surreal and just visually odd to me (not bad, it was a well-made scene, just odd) and bordered on fem-dom a bit more than I like. But of the two I preferred the Matis one to the Hive Queen one.
Neither scene is in my top scenes from the game, they are both kind of meh to me. Unlike the raider sister's scene this update which might be one of the best in the game so far.