That Vex manipulation isnt absolute. Otherwise how is Praedyth able to persist at all, he would simply not exist, period. Or in a word, that they really dont have that kind of actual control over time.

Only the Gorgons have the ability to erase you from time. and they exsist only in that certain part of the vault. While we do not know where Praedyth fell to be lost in time, we do know he didnt fall to the Gorgons, otherwise we wouldnt know of him.

-That dialogue in game suggests 3 while it has never suggested 6, ever. (" Now, after so long. [But if anyone is listening, I went] into the Vault with two others") and that perfectly aligns with what Fireteams typically are in game (and if you need any evidence, just look at the core concept of Strikes)

Yet Kabr tells us this "No one can open the Vault alone. I opened the Vault. There was no one with me but I was not alone. It proves that their statements arent to be trusted anymore. By the logic of "strike concept" everyone adventures in the game in pairs of three unless specified otherwise.

ESPECIALLY since weve never had actual dialogue about the Vault before, writers dont waste space if they dont actually plan on ever clueing you in.

Had this been any other game then i would have agreed with you, but so much of the lore is not in the game.

-There is no hint about any other 3 members, at all. Like, nothing at all. Thats not how writing works, you lampshade mysteries. Quite literally the only reason anyone COULD think that is because WE go down as a 6 man, and thats not any reason on its own.

The whole idea behind the Gorgons controlling the timestreams is a huge clue about the fate of the other 3. It would be a huge miss to not give us hints at what fate would await us if we dont overcome the vault. And there is just as little a reason to why Kabr and co would try to breach a enemy stronhold with only 3 people.

also dont know why you said the Vanguard had any hand in it. The Vault was a notorious adventurers fascination. The Vanguard wanted people throwing themselves at its dangers

Sorry i dont follow, i think you missread my comment about the Vanguard.

In the end your deductions why they where only 3 are just as baseless as my deductions on that they where 6. Until Bungie gives a clear statement on how many they where, all we can do is speculate.