If an FO is held to the same standards as a captain then they should be paid as such.
What an utterly ridiculous and uninformed statement.
A FO is not pilot in command, and does not suffer the full weight and responsibility of the flight. The PIC bears responsibility for the ultimate outcome, regardless of who may be flying or operating the aircraft at any given time, and is the final decision maker. The captain gets paid accordingly, and also in accordance with his or her seniority.
You wouldn't know about that, apparently.