The only reason why anyone would want to use two 12V-2x6 cables is to have a PC with two Nvidia graphics cards but given that ...
The MSI MPG A1000GS and MPG A1250GS are not directly compatible with AMD's RX 9070 series GPUs, unless you get an adapter.
In theory, every current pin can supply up to 575 watts, which is important for powering the GPU efficiently. However, problems can occur if the cables are cut internally or not seated properly.