It's not so much who's replacing who, or the merits or Norgaard himself. It's the balance across midfield.
A midfield grouping of Odegaard, Rice, Merino, Zubimendi/Partey, Jorginho/Norgaard is very light on creativity and flair towards the top end of the field. Odegaard yet again looks like a single point of failure in terms of creativity if he's not available. That's a general comment and I recognise the issues with form in 24/25.
On the fringes you arguably have Havertz and Nwaneri. I don't see a place for Havertz in midfield now, and his best attributes isn't creativity with ball at feet. Nwaneri I'm not even going to consider as a central midfield option just now; he seems to have issues getting minutes out wide, and if he's not trusted out there then there's not a chance Arteta is going to be use him centrally.
Norgaard seems like a good signing though. Replaces a good bit of experience in midfield and knows the league inside out. Even if the opening talks are a bit low, I can't see it going beyond a ridiculous price given the starting figures thrown around.