A couple of days ago I noticed that my graphics card’s fan was broken when I was cleaning the inside of my computer case. I got a new fan and my game performance improved dramatically. I have no idea when it stopped working; I only noticed by chance. Best I can tell, the fan hadn’t been working for a while and I hadn’t noticed because the only symptom was thermal throttling tanking the FPS of graphics intensive games. My main games being PoE and later LE, the performance degradation must’ve been lost in the noise of updates and their attendant performance changes.
TLDR: If you’re having performance issues, make sure your heatsinks are clean and your fans are working. A little maintenance can go a long way.