Interesting that the G6 seemed to be the breaking point. I have so little experience with the 109s that a similar experience with the G6 makes me wonder what is different about the G6 that I'm not understanding?
The G-6 is most like the G-2 than any other 109. Its firepower is improved, but in every other respect it's a little bit worse because of the drag penalty from the cowl bulges. It's a little slower, the climbrate is reduced, it doesn't turn quite as well, etc.
My guess is that the G-6 is more challenging because there's no one thing it does particularly well, but then it's not a total loser in any category, either. More than any other 109, you have to make good choices and use correct ACM to get kills and survive. Why is that? Well, you're flying an early '43 aircraft against the whole planeset. In the arena it's advantageous to be in a plane the turns really well, one that's fast, or even better, both. Notice the success of the Hurri II in the main arena. On paper, it's outclassed because its only trumps are turning circle and hizookas, but in an arena environment which does
not simulate WW2 combat that's enough. The G-6 is neither one of the fastest nor one of the most maneuverable. It's an in-between purgatory, and if that weren't enough, you have to be a good shot, too.