ShadeStrider

If Shulk and his friends defeated Zanza any sooner than they did, than Rex and his friends wouldn't have been able to make it to Klaus in time. Since Zanza was now dead, Klaus would die along with him.

And He probably wouldn't have caused the Titans to merge if he didn't meet Rex and Co. Before that, he was still disappointed in mankind.

So yeah, Shulk was almost a dick to the universe of Xenoblade Chronicles 2.