Want to hold your gun like it’s 1994? Doom Eternal will let you, with Classic Weapon Pose in the options menu at launch. (Doom 2016 added the option after launch, in the same patch as photo mode.)
Centred weapons come from a time before crosshairs and mouse-aim were common, when having a gun in the middle of the screen was how you lined up your shots. That changed in the mid-90s, when games like Star Wars: Dark Forces and Iron Angel of the Apocalypse first let us shoot guns while also looking at their sides a bit. It’s nice to go back when given the chance though, like when you’re wielding the old school Quake rocket launcher in Team Fortress 2.
Neither option’s 100% realistic, as the internet’s army of gun experts will happily explain to us, but it’s nice to have another retro option while shotgunning cacodemons.