The OP raises some good points about the technology of Karlach's engine. My impression from what Dammon says is that if we were on Avernus fixing it would be relatively simple and it is only because we are on Faerun that there are complications.
To me it just another example of Larian's poor story-telling/writing. Maybe it will be fixed in the next patch - see the mounting hype about 'new content' because Larian have called the VAs back in.
