Yes, you assume correct.
When you do bulk download/update of metadata it might be worth the risk to have metadata.db on a RAM drive for a short while? With proper backup, of course.
I actually mount my temp folder /tmp on a RAM drive. It seems to speed up book conversions, saves and send to disc and other things quite a bit. I assume it is because the changes to the books are made there before the books are copied to the destination.