Because HT and Pyro were trying to avoid using the same planes as WB had in the early days of AH. Instead of giving the Bf109K-4 as the "final version" of 109s, they've decided to use the G-10 with the DB605DCM instead.
The decision to use an "uncommon" 109 has nothing common with your implications: it was just because the developers wanted to do something else than the usual K-4, so naturally they picked the last Gustav of them all, which was pretty close to the K-4 in performance.
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And just exactly in what ways is the late war 109s "obsolete"?
You seem to be arguing the same things over and over again, except I've yet to see any specific comparisons in speed, agility, climb, acceleration or anything other attribute that might be considered viable determining whether a plane is obsolete or not.
Just what exactly are the grounds that you're implying it was "obsolete"?