sorry for the late reply, i read your post a few days ago i only have time for a proper answer today :-<
the thing i worry the most about show!Magnus is that he looks the same as movie!Magnus. I dont know how to explain it but with every other characters, the new actors give different vibes compared to the old cast, except Harry. The clothes are the same, the feelings are the same (and his eyeliner isn’t even as good as godfrey!). While movie!Magnus is gorgeous and perfect, he actually doesn’t fit the character’s descriptions from the book at all. Now i don’t say show!Magnus have to be exactly like the book, but with the show they have a chance to do something different with Magnus, but no they chose the safe way and create a less fabulous copy of movie!Magnus, hell, they even keep the facial hair which is only looks good when it’s godfrey (okay, maybe not, this is just godfrey’s fangirl talking, but honestly harry really looks better without it). As you said, Harry has a very big shoes to fill, and the way they chose to portray Magnus in the show will make it even harder for him coz people (well, me at least) will never stop compare him to godfrey