A subsystem itself needs multiple engineering disciplines for each. But think about the ratios of those disciplines required.

The majority of the work in each vehicle system will be performed by mechanical and some electrical engineering skills and will generally all pay the same.

The GNC folks are generally paid more in my experience but it may depend if you are mech focused (subsystems) or aero focused (vehicle performance). These all blur together and are really based on the company structure.

There’s a lot of “it depends” like others have stated, but in general I’d say the highest paid “subsystem” is Mission Systems, because it is comprised of mostly Software Engineers, who are the highest paid engineering type in the company.