Weapons affect the player's movement speed:

[yzdjmm-unturned]

When a weapon is equipped on the player's body (e.g. with a gun on their back), I think the player still needs to be affected by the Movement Multiplier, even if the player doesn't have it in their hands
Because putting the gun on your back doesn't mean that its weight is gone, but it just shifts from your arms to your torso

[CPL-M]

This could be good as an option, but shouldn't be done by default. There's a lot of cases where the speed is directly applied to the balance of the weapon.

With this, a player could hold an item on their back that has a movement speed buff and completely negate the movement speed penalty of whatever gun they're holding