Gondolin vs Numenor
Both cities, in their prime, face off in war.
Which kingdom wins?
Numenor is a kingdom, not a single city.
Gondolin is also a kingdom, but it does have one single city.
Numenor would have a hard time attacking Gondolin, because of its location in the center of a ring of mountains.
Gondolin absolutely cannot attack Numenor, because of its location in the center of a ocean and its lack of a navy.
Ten thousand soldiers were a major commitment for Turgon.
Six thousand soldiers were a pittance for Gondor in the days of its glory. And Gondor wasn't nearly as fearsome as Numenor was.
tl,dr: Numenor beats Gondolin. Not swiftly or without getting a bloody nose, but it essentially cannot lose.
Pretty much. Gondolin is vastly outnumbered by the forces brought to bear against it.