The planet with their giant super important simulation was being eaten by it (and might still be eating it, we only decoupled it from the sun)
I'm kind of surprised they haven't telaported onto it and tried shutting it down or converting it into something to nullify the sun like in the future that they attempted to make, and you gotta admit it'd make an interesting strike :p
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An excellent question ! My flip answer is that Osiris was interfering. Maybe it was a risk he had to take, Sagira. But perhaps they weren’t able to engage in space? We still haven’t seen anything like Vex spaceships, unless I’m mistaken? Or - and here is where I’d bet my glimmer - the cabal had proactively engaged the vex to keep them away? They tussled extensively on Mars - I recall some grimoire from D1 (Rasputin, maybe?) where the cabal were prepared for - and anticipating - a Vex attack/materialization. Far as I know, humans don’t have that knowledge. So I wouldn’t be surprised if the Cabal were prepared.