I don’t question your observations - i just presented mine.
So it just depends on individual perceptions.
About a year ago i saw a thread in which a Do 217 pilot complained that he got pilot sniped by a P-47 sitting more than 1 km dead behind him - the bullet penetrated the back of the plane and flew through the whole aircraft until the pilot was hit…
That’s still a niche scenario, though, and not unique to .50 cals. Plus having to hit pilot snipes (a much smaller target than literally any part of the airframe) is a lot harder.
I don’t see how the K4 is 5.7 BR. Its got the same gun every other 109 uses since 4.0 BR. For GRB its just one bomb and the flight model is not really convincing. This single 20mm cannon was good as long as mineshells were better than the rest, but now its clearly lacking.
There are enemy planes at the same BR with far more 20mm guns, using superior shells and better FM as well. Planes which also carry alot more ground ordnance for GRB purposes.
For the 109 family is just almost zero progression. One 20mm (MGs generally do nothing) and one bomb.
You should swap it for the 20mm MG151, its better than the 30mm. I don’t like the 30mm MK108 with its anemic 4mm pen, even worse ballistic, rof and less ammo.