The vex are robot versions of the flood
In a all out fight, the vex would more than likely lose.
The vex start with a conversion mind and the flood start with a single carrier form.
The flood would go for biomass, gather up and create a proto grave mind to stratagise.
The vex would start creating constructs to manipulate time or open a portal to the vex machine worlds.
Next... It gets bad.
With stratagy on their side the flood would gather large amounts of biomass until a grave mind is formed and oooohhhh boy game over man.
See the vex could simulate the flood and find a weakness but it would take just one vex construct to be infected by the logic plague...
And the vex technology is done for.
Why am I saying this random scenario?
I don't know!
I'm bored, can't do the new VOG raid and I'm tired.