I don't have Optimus hardware, but temperature problems like this are serious, so I understand the need to get it sorted quickly. You mentioned that Optimus is disabled in the BIOS, but I assume you have bumblebee installed?.... and it would be good to confirm this via the OS perspective. I still wonder if the nvidia chipset is really powered down? Can you hear fans running? (I suspect not.)
Here's an Optimus page (for Antergos), but it covers some good diagnostic steps regarding an overheating laptop. Refer to the 'Missing power off' section.
https://antergos.com/wiki/hardware/b...vidia-optimus/
It mentions testing by running these commands, and checking that the discrete card is reported as 'Discrete video card is off.'
Hopefully, after the last command the nvidia card is still off.