A lot, although I don’t have the precise figures available. While the F-35B can do a pure vertical take-off, at least under the right circumstances, it can’t do so with a useful load of fuel and weapons. It needs a runway, at least a short one, to get lift from its wings to be able to get airborne with enough missiles / bombs and fuel to accomplish its planned missions. The ski jump basically means a shorter take-off roll, if I understand the math correctly.
There are non-US NATO countries who make aircraft, you know