Why more barrels can slow a turret

Does the slower reload assigned to multi-gun turrets in naval games reflect a real design limitation?

Yes for triple and quadruple turrets, which add loading complexity, but the additional barrels can still increase total salvo and firing output.

Twin turrets should not automatically suffer a major penalty, whereas triple and quadruple arrangements add genuine loading complications. The penalty must be weighed against the extra barrels and the larger salvo delivered by each turret. The practical design question is therefore total fire output, not reload time considered alone.