I guess you are missunderstanding the "issue".
Kans ARE a threat. There is nobody denying that. They are the same threat as a unit of 6 Terminators. And because of that they will draw fire (like Terminators) which they hardly survive (again... like Terminators) because the amount of shooting need to pop these kans in not very high and if the amount of kans that finally reach melee is low, they dont even do high amounts of damage (having just a few attacks).
So they are surely a threat but lack survivability to weather the fire directed at them. And while that was also an "issue" last codex, cowardly grot does them no good either.