The kernel is okish. But compared to Linux it is surprisingly bad at a number of things. Handling lots of tiny files in huge directory trees is much slower on Windows than Linux for example. I dont know if that is due to NTFS vs ext4/btrfs/xfs, or if it is some broader issue in the NT kernel.

Some other things have been baffling over the years (but I belive they are now at least somewhat solved). For example in Windows 7 and older Windows would spend tens of seconds on "installing drivers" for a USB stick every time a new stick was inserted (or even an old stick inserted into a new port). I don't remember seeing this on Windows 10 (or 11), but I barely used those.

But yes, compared to the userspace the kernel is way less jank. (Like how Windows Updates takes minutes to run to conclude that there are updates, and dozens of minutes to install them, while pacman -Syu on Arch can be done in second if there are no updates, and maybe 2-4 minutes in the worst case of a kernel update with dkms modules being rebuilt.)