Honestly, what on *earth* was going through their heads at that point? Introduce a character in the third episode of a series, when we already have amazing villians and antagonists (ILlusive Man, Harbringer, Saren, Sovereign). Don't give him *any* development or interaction with the main character. Repeatedly give him magic plot armour shields. Have him send you stupid 13 year old trolling emails?
It's honestly like a really, rally bad fan-fic character inserted into the game. When he dies I didn't feel relish after defeating my nemesis, I felt relief because he would no longer be shitting up the game in such a dreadful, dreadful way.
Given how *well* the characters were in ME3 outside of him, Mordin and Thane in particular, he really stands out like a sore thumb. I cannot believe that the same people who wrote those characters also came up with Kai Leng.
Easily the worse written character in a Bioware game, ever.