Were there more of them that didn’t survive than anyone else on a plane?
Casualty rates is actually the easy one.
The US 8th airforce actually did do a survey of their returning crews to figure out this exact issue.
Ball turret gunners were not a pleasant place to be, but at least during combat itself, they were relatively safe, with something like a 6% expectation to be killed, and another 6% chance to be wounded.
Comparatively speaking, this actually made it one of the safest crew positions, along with the pilot and co-pilot positions.
However, there’s a few things that do skew this data a bit. Namely, this only takes into account the crews that flew back to base.
This means that bombers that failed to return to base and had crews who were forced to bail out wouldn’t be in this survey data, and this is where we need to do a bit of inferring.
(Diagram of the interior of the Sperry ball turret)
Something that needs to be acknowledged is that if the aircraft was significantly damaged, the ball turret position became infinitely more dangerous, as it was the only position aboard the bomber that couldn’t be manned while wearing a parachute.
If combat damage caused loss in electrical power to the turret, the gunner would be trapped unless or until a crew mate managed to manually crank their turret into the vertical position.
Equally, if the aircraft took damage that resulted in an uncontrollable spiral, skid, or any rapidly deteriorating flight state, the gunner would need to first rotate the turret to vertical if able, unlock their hatch, disconnect from their only available oxygen supply, climb out, run to grab their parachute from the radio operators area, connect their parachute to their parachute harness, and then run for the nearest opening to get out of the plane.
So while among aircraft that were able to return, the ventral ball turret is one of the three best positions for its survival rate, if your bomber went down, an event for which data isn’t readily available for, its far more likely you went down with the plane.