The G6 we had before the 109 updates was a late model with a galland hood, I believe. This was before we got the G14. The 109G6 was given the 30mm option to be competitive.
Definitely, a LOT of G-6s had the Mk.108, and 1/3 of them had this gun, but that's counting the many many later models of G-6. What we have here is the early style with the early canopy, and the early weapons package to go with it. This way we can have a 109G in a 1943 scenario use without having the un-representative 30mm gun option.
Now that we have 200 rds for the nose gun, too, there's not much to complain about on the G-6!
P.S. I thought the G-2 already had WGr 21s