The sums involved are not even that high for high performance sales roles.
This seems really penny pinching from ServiceNow, but we know they like to penny pinch when it comes to things like UX and UI design too.
I presume his base salary reflected his targets as well. If they want to raise his target, they need to accept that means he needs a higher base salary to reflect that.
I suspect that he will win this in the end. In the meantime I expect record low sales for the company due to motivation issues.