Why is the gunner still exposed?
Ayn Galt

He isn't? Thats the comander turned out as standard operating procedure whilst manoeuvring in a low threat environement.

The “gunner” would operate the Samson RCWS (Remote Control Weapons Station) usually fitted with a M2HB QCB or M3P clearly seen in the photograph

This could be replaced however with a wide range of automated weapons stations fielding anything from a Fn-Minimi/Mag up to a 25-30mm Autocannon or 40mm High-low AGL. Depending on how much troop carrying capacity you are willing to cut.