Why are you so focused on heatsink paste? I gave a half dozen other perfectly valid examples and yet you've decided CPU paste is the one that matters? CPU paste issues are valid, not just because they're dry, sometimes they're also fully missing and nobody would really notice unless the system is actually stressed.
Howabout you expand your next reply: you've yet to touch on the number of hardware permutations which can exist even on a "modern" PC. Literally hundreds of CPU options, dozens of chipset options, hundreds of system boards all with their own funky firmware decisions, bordering on hundreds of GPU options, dozens of sound options, thousands of network options, dozens of storage options. Every one of these points on a hardware decision tree matter when chasing down a game that's doing something "wrong."
Or we can talk about each one of those pieces of hardware likely needing one of dozens of different driver versions. In most cases Microsoft can find a driver for you, however the MS version isn't guaranteed to be recent or fully featured. The manufacturer will near-always provide their own driver package, typically replete with a bunch of tertiary software which claims to enhance your experience with their product. My Logitech keyboard uses a different "fully featured" software package than my Logitech mouse, so I have two continually-resident software packages just for those two devices. Turns out, BOTH of them have integrations where they track which app you've got open to then offer keybinding or RGB color options unique to the app. Then I've got another continually resident software package for my Soundblaster XFi 4, which is a little wonky and sometimes drops the Dolby Digital encoding via SPDIF, which I usually only notice when my rear channels stop functioning. Then I get to play the game of opening device manager, right-clicking to remove the XFi audio driver, reboot, let the system reinstall the drivers auto-magically, then go back to the software configuration package and re-enable DDE via SPDIF, and finally change my default output to the SPDIF again. After all that bullshit, I haven't even come to the point where my GPU driver occasionally needs some love to avoid issues in games, or my network driver needed an update for TCP stack overflow issues when using 2.5GbE mode and after transmitting something like 16 terabytes of data during a single power-on session (I don't power the box off, and centralized backups are a thing in my household.)
Or we can talk about OS versions and updates, which we ALL know are perfectly stable and haven't caused issues with CPU performance, or application stability, or hell even boot process failures when mixed and matched with other certain drivers or hardware or resident applications. If you'd like to skip that, we can talk about whatever dorky applications are already installed and have hooks into the underlying OS -- DRM enforcement, anti-cheat nonsense, howabout antivirus even? I'm sure nobody here got hammered by the Crowdstrike EDR update which BSoD'd about a hojillion Windows machines two months ago. /s There have been plenty of examples of 3rd party apps screwing with games since the beginning of PC time.
And in the other corner, for an example, the Series X has a singular highly controlled hardware ecosystem which only deviates after having been QA'd to death. Supply chains for that hardware are tightly controlled, firmware versions on hardware devices are tightly controlled, the driver and OS updates are rigorously controlled and coordinated. The user can't install apps at an OS level, they can't screw with the OS config, they can only download or otherwise install a game that has been purposefully packaged to maintain isolation from the other loaded games and OS features.