What differences? You never answered that question at all, so I'll ask it again: Which handling differences (that are modeled in AH) are not a direct result of engine or armament changes (weight, bulges, torque, CG etc.) in the 109G-2, G-6 and G-14?
This question paraphrases as "Besides all the differences that make different versions of an airframe, different, how are they different?"
It is an impossibly loaded question in the same way that "When did you stop beating your wife?" is an impossibly loaded question.
Even then, it was answered at least once when somebody posted about the different cockpit hoods each of the three have in AH.
You can't just take the engine differences off of the table. They are huge and are usually the single biggest performance indicator of an aircraft.
The P-51s are just as well represented in their service period as the Spitfires are. Basic coverage is there, but significant holes remain. I am sure that is true of the Bf109 and Fw190s too, but am not that well versed in those aircraft.
The fact is that the P-51 only came into it after the work had already been done, first by the Spitfire and Hurricane holding the line and then by the P-47 destroying the Luftwaffe. Yes, P-51s fought, but it was all but over when they showed up in significant numbers. It had a much shorter combat career as a first line fighter in WWII than did the P-47, F4U, Spitfire, Bf109, Fw190, Yak, Ki-43 or A6M series and thus in AH is represented by a smaller number of versions.