You are not a assassin jungler if you can only last hit enemies with 20% health.
Basically these "assassins" will only go in when their team is winning massively. Because their team doesn't even need them to win the game they have the tendancy to have around 10% kill participation, with extremely low damage as par as a support. I seen so many Kha'zix's who adopt this playstyle and make are loss granted because they will only attack if we are straight out winning.
Being a grasshopper is one thing, but being a leech is another.