Talking about a fully mechanically controlled airplane this makes no sense at all.
Makes a lot of sense.
In a "mechanically" controlled 737 (as you said it) dual input is very much possible. I suggest you update your knowledge - it is possible in
ANY Boeing. If actions of both pilots are sufficiently different and forces exceed some limits - both sides will be separated, this was done to counter possible jamming of controls on one side, certification required such a solution.