Okay, but The Borg have comparable numbers. Humans are Species 5618 when the Borg make first contact. That’s 5617 species they have assimilated (or, at least, tried to assimilate) beforehand.
In Voyager, the whole Delta Quadrant is teaming with Borg. Functionally on par with the Zerg.
Assimilating a single Zerg doesn’t change the fact there is 10,000,000,000 more of them rushing in.
Okay, but The Borg have comparable numbers. Humans are Species 5618 when the Borg make first contact. That’s 5617 species they have assimilated (or, at least, tried to assimilate) beforehand.
In Voyager, the whole Delta Quadrant is teaming with Borg. Functionally on par with the Zerg.