The Gorgons are not taken. Just like you said, the Vex have the ability to bend reality and time to their desire as much as they want within the confines of the Vault, while outside it's not possible. The Gorgons are protecting the Vault of Glass- aka the Glass Throne where Atheon is. If they believe you are a threat, they will erase you from existence. You will be totally forgotten.
Side note: Kabr was not forgotten because he left behind a legacy that tells of his story. Praedyth is trapped somewhere in the dark corners of Time, and Pahanin managed to escape. If there were more than three at the time of their demise, they were likely totally erased from existence with no legacy to leave behind.
Oryx can bend reality in the Ascendant Plane, and he can to some extent in the physical world by taking (ripping a living creature out of the physical world and into his own dimension where they are seduced and wholly consumed by Darkness). Honestly, I see this theory everywhere that the Gorgons are Taken, they're definitely not, and people aren't taking into fact that VoG chronologically speaking, came way before the events of Oryx's invasion (not to mention if you look closely at one you'll definitely notice it's not taken).
People should also take into account that if Harpies could be taken, they'd show up anywhere Taken Vex can be found and you'd DEFINITELY find them in the Paradox mission (but did you notice they're NOT in the labyrinth during the mission, or anywhere else???). It's likely the Gorgons attempted to face the Taken who invaded the vault, and realized they couldn't erase them- so they likely either were destroyed or they fled to somewhere deeper in the Vault where the Taken haven't found yet.
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You really need to use some more critical thinking.
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Let's recap shall we? Oryx can only take LIVING beings. Harpies are the only vex subtype to not contain a biological core. A gorgon IS a glorified harpy. The only one who needs to use critical thinking here is you, a person completely oblivious to the lore.
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Oryx and the Vex have a beef that goes WAY back.
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They're not Taken. Go see for yourself. Read the grimoire. Play the game. If they were taken, they sure as hell would've appeared at SOME point during the TTK campaign or one of it's many post-campaign quests. They don't. They don't even have the same look.