Works!

Thank you so much. I have no idea what went wrong before, but I assume the problem was somehow related to extracting/copying the files from the jffs2-file:
IIRC, it did this only once and used they resulting files for all my attempts. I was so sure that I needed to find the right parts from initfs to go with the rootfs that it never once occured to me the cause of the problem could be something completely different.