Are you on about Artillery gun crews, anti-tank gun crews or battalion gun crews.
Different training , skills and missions. Battalion gun crews were primary infantry trained and then specialized in battalion guns.
Artillery as it says on the tin with infantry training, anti-tank crews probably a mixture of both as a generalization.
I would of thought using gun crews to fight other than their dedicated mission work well for a skirmish game (Bolt Action) but maybe not so well for the larger style games (Command decision).
Speaking for Rapid Fire games generally my artillery/ battalion / anti-Tank crews do not get close enough to the shooting to use their small arms, if attacked they can defend themselves with small arms, however they would not be able to fire their main gun or if they had fired their main gun they would not be able to fire small arms that turn. As for re-deployment that would have to be written into the mission brief before the start of the game.
The question is what are the mission priorities, fire big gun or shot small rifle.
I am with you I would have thought they don’t magically transform into an infantry squad unless you are playing a Kelly hero’s style skirmish game. Using these crews any other way is just being an over active war-gamer falling into the habit well are all guilty of at some time or other, I want to shoot so I am going to shoot.