I’d argue (from a Watsonian/in-universe perspective) aliens as they’re typically portrayed in sci-fi are “unevenly advanced”. They have the technology to cross the stars, but are somehow otherwise very primitive.
A good example, there’s one sci-fi story that consciously acknowledges this. Basically, aliens show up and are actually armed with muskets. Turns out, FTL travel was the only advanced technology they had.
In the sci-fantasy setting I made, there’s a similar explanation. Humans are the only civilization to invent transistors. When humanity is first invaded by aliens, they initially have great success, but are ultimately destroyed by an artificial superinteligence humans created.