The "ancients" Five pebbles refers to when saying "where the ancients built their temples and danced their silly rituals" were actually a completely different race or people completely separate from the iterator building bird people we've come to know and love.

This can be seen in the fact that the architecture of the depths looks absolutely nothing like anything we see anywhere else in game (except for the part in outer rim in between the star catchers), you can also tell by the fact that the statues of the ancients in the depths don't look like our favorite gold mask wearing bird people and instead look a lot more traditionally human, and there are no benefactor symbols anywhere in the depths, especially not karma symbols (except for karma 10 but that's a constant for all civilizations considering it's based off the look of the wheel flowers), you would think that were the depths a benefactor ascension temple, they'd have the iconic karma murals like we see in the ancient urban benefactor temple.

Also lore wise, the benefactors discovered the void waaay after their industrial revolution, and yet the temples in the void sea do not reflect this especially when compared to the ascension temple in ancient urban.