All the best stuff is preadapted for other species, and it's up to humanity to figure out ways to adapt things that have been through millions of years of evolutionary design, based on fundamental principles that people are still trying to figure out. As humanity figures it out, the human-designed stuff works well for humans (as well as human engineering and QA can make it), but is much less effective than the standard galactic designs.
Just as there as Assholes Who Don't Get It among humans, there are Assholes Who Don't Get It among the galactics. They're the antagonists. They mostly don't engage in exponential expansion, but they have terrible habits like denying the free will of other intelligent species: eating them, puppeting them, enslaving them. Because eating cloned tissue and puppeting shells and being served by subsentient AIs just isn't the same as the good old days when a byakhee was a real byakhee.
Humans, of course, can cause cognitive dissonance among aliens just like the aliens do among humans. A loud Hawaiian shirt tends to freak out predator species that rely on stealth and camouflage, for instance. Rigid endoskeletons are icky to tentacled beings with hydrostatic skeletons.
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