I have no proof for the others, although it seems that it is not just ER in question.
pk is not a problem. The problem is the behavior of MP players. In five hours on the server, 50% of the world's population of combat aircraft is destroyed. Fearless behavior drags and frivolous use of weapons. If behavior changes in the percentage of aircraft destruction per hour, in real life, immediately the use of weapons is different where Pk is large at the right moment.
Although there are problems in radar operating modes, and guidance problems, countermeasures ... indisputable!