Indeed, it was always the most likely.
A slower system to get used to, maybe, but you will get used to it over time. Slow is better than crashing; at least this allows a level of confidence in the machine you haven’t had for a while. Perhaps you can rename the profile to “Slow and Breezy”. 
Regarding the Samsung 980 Pro;
The firmware might go some way toward allowing you to regain some of that performance loss; if what Tuxedo Support tells you, is accurate.
It is also possible that only the range of drives specific to the firmware will be detected (a guess). Make sure you have the exact firmware for your drive. There is an ISO on the Samsung site listed under Samsung Storage Firmware – NVMe SSD-980 PRO Series Firmware – ISO 5B2QGXA7 | 27MB that appears to be the one. Is this the same as you downloaded previously?
Related:- I found this article at Toms’Hardware Samsung Issues Fix for Dying 980 Pro SSDs, which is disconcerting in itself.
However, it also states:
It should be noted that 980 Pro SSDs running the 4B2QGXA7 or 5B2QGXA7 firmware are not affected by this issue.
So, the 5B2QGXA7 previously linked seems to be the correct one, if it isn’t already applied.
Samsung also recommends that it be installed using Samsung Magician Software; only Windows, macOS and Android versions are mentioned. Here is the Installation Guide (for Windows).
Of course, these are not much use without Windows or macOS.
It might be possible to use the Samsung tool via a Windows PE boot disk; such as the Hiren’s BootCD PE (Preinstallation Environment). However, this is likely outside the scope of the Manjaro forum.
As overheating is now recognised at the culprit, it’s probably time to mark this thread as solved. Check the tick under whichever post you feel initially led you to this conclusion.
I’m glad we could help. Cheers.