With the current stage of the game, its nearly impossible for non-pk'ers to get anywhere near the pk achievements, especially the killstreak ones. Maxed out clans and teams just camp wildy spots all day, and with only 1 world theres no way around this. Yeah theoreticly everyone could do this, but i dont think its intended you need a team for the achievements cape. Sure, i could try getting decent at pking, but even then i wont ever win from a 6 man team in maxed gear, that sits in wild all day.
I suggest: adding other options to the killstreak achievements, such as killing a certain boss without taking any damage, or killing a amount of bosses without dying, stuff like that. This way the player will have a choice to either go pking or go pvming.
With keeping the kill 50 individuals achievent, you still force players to explore pking, but this makes it so they are actually completable, and players know that at some point they will get to 50.