Nick's senses had not been heightened yet when he first fought the captain. That, along with the fact that Nick has practiced and perfected his fighting skills since then may contribute to the difference in his anticipated performance against Kenneth.
This idea is a little out there, but what isn't about the Verfluchte Zwilingsschwester? Whose baby is Adalind carrying? Hers and Nick's or Juliette's and Nick's? Juliette did think she was pregnant for awhile, and Adalind had no clue she was until Henrietta told her. Maybe the spell has lingering effects of sorts? Lapses of identity with big time identity crises?? No matter how much Ms Adalind claims to love her baby(ies), I still find it hard to accept that she was willing to give up her powers so easily. No matter how afraid of being killed by Juliette she claimed to be! Maybe she knows more about the effects of her spells than she has told; there has to be some form of personal gain in it for her. Otherwise, she is more out of character now than anyone! Just a thought, however preposterous! :)