DSII question

Afternoon (or evening, or morning, or whatever time it is in your
neck of the woods),

Have a DSII question for you that I'm sure someone somewhere in some
distant past, place, dimension knows ('cause I can't find an answer
in the rulesbook).

Can a tank (element, whatnot) fire a GMS in addition to it's main
weapon in a given turn? And if not, what's the point of mounting
GMS' on tanks with weapons that out-range the GMS'? (and hit better,
etc).

For example, say I have a tank design with an HKP/4, Enhanced
FireCon, and a GMS/L enhanced. Range of the GMS/L is 36". Medium
range of the HKP/4 is 36". Both have the same to hit chance (D8).
Both draw the same damage chits (red/yellow). However, the GMS/L
can be spoofed, intercepted, knocked down, etc, whereas the HKP/4
does not suffer these problems. AND the HKP/4 draws 4 chits, whereas
the GMS/L draws 3. What's the point of carrying a GMS/*, then? Is
there some hidden thing I'm missing about GMS systems? (the answer
is "yes, obviously" to those who know ;-)