The best bullet proof glass made at the time of the 109s was made flat, which is why the framing.
So say what you want, but when rounds were pinging the windows, the early style might have been better for the pilot.
Further more, curved glass, in those days produced more distortion, even if flat at an angle.
Hence the steep front window of 109s - least distored view in the whole set of all ww2 planes.
Luft had all the aces: required pilot, plane, straight flying deadly amo, bullet proof glass, and least distorted windows.

For which 109 that I would like? g10as I guess. g6 was the most kills plane tho, not sure why not in game.