In my opinion, like Comyt said, it depends on the person.
There are those who are good at 1v1 and good at GS.
There are those who are good at 1v1 and bad at GS.
There are those who are good, but not neccesarily elite, at 1v1 and good at GS.
There is the aspect, as an individual, of knowing what you have to do to help your team in those minor movements. That doesn't exist in 1v1.
By the same token, in a 1v1, neither of you have anyone nearby to help, and neither of you have anything to focus on other than each other.
Based on this, I'd say 1v1 takes more skill to be good at than gs, hence why I think there are people who are good at GS that aren't as much so in 1v1.