These complaints are somewhat valid and also not exclusively Windows things. I've experienced similar issues on every other major platform.
> When copying files, copy progress dialog is sometimes opened hidden behind all other windows
I've not personally experienced this. If you initiate a Copy and then change focus, the dialog will not steal focus. Perhaps that's what you're experiencing? I despise when apps steal focus (i.e. Outlook 2015/Skype 2015 splash screens) and so I appreciate this aspect of it.
> The ui formerly known as start menu populates search results incrementally, so Win+program name+enter can open different thing based on timing
That happens to me constantly on Windows 7, this isn't something new. As of right now, if I type "windows update" in the Win7 Start Menu and hit enter it launches "Lenovo Update" on my laptop. If I wait then I get an Apps list of Lenovo Update, Java Update, Intel Update; then gradually documents, downloads, One Drive searches, and then at the last moment "Windows Update" appends itself to the bottom of the Apps list.
> Randomly self-reboots at night, breaking long uploads or batches.
There's nothing random about this. When an update is installed that requires a reboot then Windows notifies you that it scheduled a reboot outside of the Active Hours you defined. That notification sits in the tray until you manually dismiss it. You have the option to click on it and open the "Restart Options" menu which allows you to put off the reboot for up to 7 days.
If the update is installed while you're not present and you never return before the reboot is scheduled to occur then I'm going to assume it reboots. I would like to say that it holds off the reboot for up to 7 days for you to return to the PC but I don't believe that to be true.
> Force-installs drivers (NVIDIA, synaptics, ...) that crash on current setup or lose features. Even during the work.
Windows will install baseline drivers for hardware that doesn't have a proper driver installed. These drivers do not necessarily have the full functionality of drivers you download directly from the vendor, however they are provided by the vendor. If you've installed a driver directly from the Vendor, Windows will not supersede that install with the Windows Update Version but will instead list the version in Windows Update as available to install.
> Randomly resets file associations.
Windows Media Player on Windows 7 is the only time that I have experienced this issue. I don't use any of Microsoft's preferred Apps (e.g. Edge, Mail, Groove, etc), I have different defaults associated, and I have never had this happen. I have had an issue where x86 and x64 versions of Firefox were both installed and, when I uninstalled the x86 version, Windows notified me that it changed associations back to Edge since the x86 install was set as the default browser. The notification was not temporary, it sat in the notification tray until I manually dismissed it. That behavior is perfectly reasonable to me.
> Resets some settings to default on upgrade.
This is true of lots of software, I've had it happen with Chrome, Firefox, and iTunes with in the last 6 months. It doesn't always happen with Windows and it doesn't always happen in other software, but it happens. I cannot recall this happening to me in Windows 10 other than during a major update to a product. Specifically when they made significant improvements to Cortona and wanted you to give it another look, in that case it reset to the setting from disabled to "setup and configuration" mode but it didn't enable Cortona.