As I mentioned, offline testing. Since I keep having bad luck with tanks spawning to us (Rook/times I'm on), and the rarity of the Tiger and King Tiger in general, I did testing offline. I have only ran into 1 T-34 since the G-2 was released, which I augured pushing a bad angle, and I haven't seen any Tiger's or KT's. I'm having bad luck in my hunts.
The G-2 is the only thing I've been flying to date (in terms of tank killing. I do have 1 sortie in the 25H, which is another plane I use for tank killing, but I did not use it for that purpose). That in it's own would indicate that it's my primary tank killer now. Just because I'm just having crap luck in getting me some tanks, doesn't mean it's not my primary tank killer.
I do wonder if there isn't some slight variance between offline and online though. A while back I did a test with the Il-2 using the 23mm guns and found that you can destroy a Panzer with them, it took about half my ammo, but I managed.
I got lucking one night and ran into a Panzer when I upped an Il-2 with the 23's. He wasn't moving and he even ignored me and kept shelling the town. So I got the angles I used offline (which would normally have gotten me blasted by other tankers). I pumped all my ammo into him, nothing. So yeah, I wonder if there isn't a slight variance between offline and online.
I did this before the Panzer was updated mind you, so it may be different now.