I understood what you meant first time, and I'd agree with you but then we'd both be wrong.
If the fluid boils, you have no brakes. I agree completely. Changing the fluid makes no difference, I disagree entirely.
So we're agreed that you have brake failure with boiling fluid. We're also agreed that brake fluid is hygroscopic, it absorbs water over time... Yes? Old brake fluid boils at a temperature 80 degrees Celsius LOWER than new brake fluid. Therefore, you have a greater chance of suffering total brake failure with old fluid, than you do with new fluid. It's really not a difficult concept.
Clang!....... Ah yes, NOW the penny has dropped