There is a book you can read after defeating the main boss fight during rescue of Gondians in that same final room, which explains quite detailed how their giant two legged machinery really works and...
It has to do with tad poles, zombie parts and just a refurbished automation to stuff them up with necrotic and illithind power by shoving those big tadpoled body parts into each corresponding metal part, like not as much to do with infernal machinery other than the infernal metal to make them extra durable, like if it wasn't for getting refurbished it was meant to be operated by a living gondian from within,
this would not have provided answers for Karlach and might be why concept around them wasn't realized into a gameplay content to reflect Karlach's storyline, perhaps we would have had that with content planned for Act 2 that just for unknown reasons didn't make it into final game, I'm not even sure if they even really went as far as to start creating a map level for it beyond the concept of idea, had something to do with Vlaakith's temple area in the hells, is not even sure where it would have been fitted in between the last two acts but the interview suggested Act 2.
But all in all I would also have been sated if there had been more weight into Karlach's story to potential showcase and explain with help of a cinematic scene as to why any potential fix could have failed and suggested finding the solution from the the actual forge where Karlach's engine was made in, it would have been a nicer link to the epiloque part as well.
