Wow, your post seemed to have come out of nowhere judging by the stuff that has come before it. It seems you've started explaining something from the middle rather than from the start. What plot-hole are we addressing now?
Speaking of fallibility, you've also highlighted something quite interesting in regards to Kerrigan in general. If Kerrigan is supposedly the ultimate and 'bestest' thing of all time (she must be now because WoL pretty much elevates and rubber stamps her extreme importance in defeating the biggest and evillest thing ever! ), then why is she incapable of doing something arguably more simpler (compared to prophetically being the only person capable of defeating a universal and seemingly omnipotent enemy that is) than exterminating a few Dark Templar and what does this really say about her actual importance and ability in defeating the DV?
A disconnect between yourself and the reality of that in-universe is what you get, which is exacerbated when you have characters with actual hyper-inflated importance when there was none before. The Overmind in SC1 was represented (note that I don't say is) as such up until it was proven otherwise by it being killed because its plans didn't ultimately work out. This was one of the beauties of the Overmind's character - despite all it's bluster, power and aura, it was still fallible. WoL, however, seems to have re-instated this hyper-inflated importance and the sense of "everything I touch is gold" for the Overmind by "nudge-nudge-wink-winking" that actually "everything that has transpired has been according to my design".