Totally agree o.o when I didn't know English, it seemed like writing in Swedish was just fine, but now a days I just can't get a good tone to my stories if I write them in Swedish D: I nail essays like a boss though :D
Compared to English, Swedish does feel a bit more childish and doesn't come across as that serious to me, and for someone who's waaay too into the dark stuff, Swedish sucks. Romances are even worse xD reading a love story in Swedish just makes it feel like the characters are ten year olds even if they say the exact same thing as in the English version. I dunno. It just sounds wrong. My ancestors must feel so betrayed.
I did write lots of stuff in swedish before, mainly for school. While I don't feel like I catch the atmosphere properly, I did make my teacher gag once when he read my story about a school shooter out loud for the class. (another story he read was made by a classmate was about a bussbombing. You wouldn't get away with this shit in the US xD) so I guess I can get the atmosphere right, I just don't feel like it becomes as powerful as English writing.