You’re really missing on the simplicity and speed of the CLI and a sudo nano /path/to/the/directory/name_of the_file > write or paste the text with Ctrl+Shift+V > Ctrl+O to save > Ctrl+X to quit. You could also do a half-way GUI/half-way CLI by creating the file in your home directory with your favorite editor, then sudo cp -v /home/you/your_file /path/to/the/directory/it/should/go/, but if you want to do it the full “GUI and as root”, I recommend you to read those pages:
Kate seems able to handle it, but I can’t confirm this, as I’m using neither KDE nor Wayland…