"Sorry, but not correct.
The AMM (Aircraft Maintenance Manual) says:
...The CAPT and F/O stick orders are algebraically added..."
Agreed with totally! The output is always the algebraic sum of both sidesticks....e.g. Capt inputs 12 degrees left turn and F/o inputs 6degrees left turn....because they are both in same direction, the result is a 18degree left turn.
Likewise a 10degree input to one sidestick with a 10degree input to the other sidestick in the opposite direction cancel each other out.