Back in the 00s, a story about CPUs getting so hot they'd start on fire went viral. In it was a video of someone removing the cooler while it was running and then a few seconds later a flame appears.

On the one hand, obviously you shouldn't remove your CPU cooler while it was running.

But on the other hand, fans and mounts can fail, so this was still a risk even for people who were smarter than removing the cooler entirely.

It prompted CPU makers to add thermal protections that started out as "if CPU hits threshold, cut power", but over time more sophisticated heat management was integrated with more sophisticated performance and power management.

So these days, if you aren't sufficiently cooling your CPU, it won't die much quicker, instead it will throttle performance to keep heat at safe levels. OP would have gotten better performance out of it after removing that plastic. Assuming it was CPU bottlenecked in the first place. Things like RAM choice and settings can make it a moot point because the RAM can't keep up with the CPU at 100% power anyways.

I didnt have the analitical skills at the time to test its performance as i was ~12years old, but i remember it always ran full speed CPU fan and only very occasionally shutdown on overtemp, once i removed the plastic it went back to normal/expected fan speeds. It was probably the AMD Athlon generation CPU from memory, so it probably wasnt being pushed too hard to perform, mostly running Snes emulators and sim city 2000 probably.