Actually, the Winchester Model 21 was introduced in answer to the Remington Model 32.
That would be a pretty hard premiss to prove. Both guns were under development at the same time, and within the Patents and factory drawings there are both side-by-side and over/under versions of both. Throw in Winchester going belly up and being acquired by Western Cartridge Co. and the Olins; the Depression; and Remington pocket catalogues of the period that introduce the Model 32 being undated; and it getss pretty muddy.
Is there any documantation that says Winchester and Remington came to an gentelmen's agreement that one would bring out a side-by-side and the other an over/under?