well maybe bad writing is not entirely to blame. have you ever been terrified? all your skill, speech, control, knowledge go out the window... humans die to wesen easily because they're terrified when they reveal themselves or are usually snuck up on and boom.
Hank was nearly undone by the reality of Wesen, now he knows they are real, he can at least offer resistance. I still think he comes off as too good, because wesen are supoosed to have supernatural strength and enhanced attributes.. altho it depends on the wesen.
Also Hank will know he has to try that much harder against wesen so it's not just a normal fight, you gotta put your game face on and really determined.
I think part of what gives NIck energy is that Grimms have a hatred reaction, and emotional reaction to wesen, you know like when you powerfully love or powerfully hate your attacks are always that much stronger.. I think part of the Grimms strength is tied to his emotional connection - evidenced when Nick loses his Grimm sight, he is actually weaker.. now he didn't stop being a Grimm, he just stopped seeing the wesen vogue. They describe how the eyes go black on a vogue, like a stone cold emotion coming over them, the unnatural nature of the wesen must really rub Grimms off the wrong way.. and it just sets them charged.
And yes, he is friends with Munroe, Rosalee and other wesen, but you can manage your emotions, and when you have a friendship connection you're not going out to kill, the physical reaction that is fuelled by part emtion disgust/hate is not uncontrollable,.. it's powerful, but not uncontrollable,
I would think that Nick actually enjoys slaughtering/beating wesen it gives a relief, the sort of feeling you get when you've eliminated a real threat of reduced the amount of evil in the world.. i mean evil should make a human being really riled up and itch that cannot be scratched until you get rid of the evil, and the wesen trnasformation and state is all the more intensifying to a Grimm, and being a cop, he gets to come across a lot of evil wesen, and can unleash his full fury, something he won't do on his friends, because he's not fighting them. Notice how in the earlier seasons he had trouble controling himself from slaughtering the criminal wesen.
It took a lot of self control and all his training as a cop to be able to stay his hand, this makes Nick one of the best Grimm's because he can exercise control over his physical tendencies..something many wesen struggle to do, which is why they have to keep killing humans or slip up a lot.
Saying that, I also think there is a supernatural power to a Grimm, like the wesen have, but opposite, almost like God's balancing of the aberrations. So it's not just emotional, but the emotion activates or amplifies a strength in the Grimm that is super human - to me it's like one of those parts of the brain that are dormant in most people are active in Grimms, and it lends them the extra capabilities.
Nick did get a booster from the Zombie encounter that's permanently a part of him, but they don't play it up much any more, no more or not many high octane fight scenes sadly.
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btw.. did you notice how they did search for Trubble at all this episode? like they forgot about her, and we'd have to if the writers didn't show her coming out of that cage.
She looks like she's co-operating with them now, i wonder what they did to her? I have a feeling they trained her further,
And Wesen have serious trouble taking on Grimms, which indicates that whatever enhances Grimms, it's top stuff, superior almost or at least more advantageous to have than what the Wesen have.