Didn't the 17 Pdr's used to be able to see icons when in F3 mode? Maybe there is some sort of cross over effect and HTC just did a quick fix. Not sure. Only they can answer that.. 
All guns were, that's why F3 mode was taken from all the guns. But you still can look around while mannign them.
The 'stiff neck' has another reason. What's maiking the 17lb different from all the other manned guns is the fact it has a regular sight like any regular tank gun. Thus it's being treated like a regular tank gunner position, and all of those lost their ability to look around when the tank modeling was changed.
That's why adding a "commander" station would be the esiest fix, and not a particular unrealistic one as well.