Another idea regarding Kumoko and the demon lord:
-We've been led to think Kumoko is now that mute girl sent to kill and that she's now an underling to the demon lord.
But what if she's in fact the one controlling the demon lord ?
Far in the future, her skills would just be out of this world, probably administrator or game/world creator class.
She might use the demon lord as a puppet to pull the strings without being noticed.
Let's not forger she knows that world is doomed and she's probably trying to find solution, as is the demon lord who also got access to the same revelation.
There's control, but there's also working towards the same goal. That could work with what we've seen from the present timeline.