nothing wrong with using ice block tbh in my opinion. it just making use of all the game skills and mechanics, think of it this way, in order to get ice block, which would have limited use against KJ normally he had to sacrifice a skill point which would have increased his damage, therefore he sacrifices damage for security. What he is doing is perfectly legit and they deserve their first kill status.
If you remember the same argument came when nihilum killed Vashj, everyone saying it was a exploit that allowed them to kill here, no it was making use of game mechanics and a bit of luck.
In order to use this as an exploit the user would have to have a high degree of luck on 2 accounts, 1 to time it perfectly so kj did the summon while they were iceblocked. And 2nd that kj even focused on them. chances are KJ will focus on 1 of the 24 other people in the raid