nah, you vac so they can't react, then while they're getting pulled you wall
game is patching
it's source 2
See my edit, I agree it is safer, as it allows less time for them to disable you, but wall first lets you guarantee the wall damage.
Because of the cast point on wall, it allows them about a half second to disperse after being vacuumed(and that's if you shift queue), so you aren't guaranteed to hit everyone with the wall as you would be in the reverse order.
It's more situational though, if you are in a choke point where they have no room to disperse then sure, vac first to be safe, but its not like the reverse is incorrect. Also this is assuming that you don't ideally have a secondary disable to follow up the vac, in which case vac first is always better.