Except the F35 is designed to kill it's targets at ranges far in excess of what the 25mmp) cannon can reach, in other words, if the F35 is overflying its target something has gone wrong with the mission...
Well, ***** happens. I would rather have something as a backup just in case.
The US already learn't this lesson, why they are intent on learning it again I'm not sure.
I understand why the B has a gunpod (most versions of the Harrier also have one) but I'm not sure why the C does.