But those guns do make a big difference, if the k4 had a 20mm, it would also prbably be perked.
You mean multiple 20mms. I usually fly the Yak-9U and its 20mm is supposed to be the best shooting 20mm in the game, but it only has one of them and it takes time to take your target out of the sky with it unless you get a pilot kill. In fact a lot of pilots are completely willing to give me a crossing shot gambling that I won't be able to hit them hard enough to matter. One 20mm won't make it perkable, especially with the 20mms available to German AC, more than one means no spinner cannon.
The 30mm is an advantage to the K4, not the only thing keeping it unperked. It has the engine power to stay out of the fight, wait for you to shift your attention, then dive in and hope for a hit, knowing it can climb away if it missed (thus the untouchable flying timidly comments). Its my opinion that any aircraft that can be flown such that its untouchable except by perked aircraft should have a low ENY, certainly not 20 ENY.
Also I support the idea (and I've mentioned this idea a few times before) that ENY should vary tour to tour based on popularity in the previous tour. Aircraft flown all the time should have a low ENY, those mostly ignored should have a high ENY. This will result in "bargains" that change each tour, resulting in seeing more varied aircraft overall, and make the game more interesting.