This reasoning obviously cannot compensate for a difference of more than 10% or so.
And in my experience in most places software contractors are paid more. Contractors are simply the people who are good enough to be technical people who demand higher salaries at non-FANG. They don't get, and don't have a need for, job security and in trade get a lot more dineros. This can be because of specialized knowledge (e.g. knowledge of bank protocols and encryption, including the softer side of it (ie. what particular kinds of encryption actually protect against)). These people are not needed often, and not constantly, but when they're needed they're critical. Hence, lots of pay, switch from bank to bank often. This exists for specialized mechanical engineers in defense too, for example.
And in my experience in most places software contractors are paid more. Contractors are simply the people who are good enough to be technical people who demand higher salaries at non-FANG. They don't get, and don't have a need for, job security and in trade get a lot more dineros. This can be because of specialized knowledge (e.g. knowledge of bank protocols and encryption, including the softer side of it (ie. what particular kinds of encryption actually protect against)). These people are not needed often, and not constantly, but when they're needed they're critical. Hence, lots of pay, switch from bank to bank often. This exists for specialized mechanical engineers in defense too, for example.