The reality is that optimizing for the common scenario just gives such significant benefits that the worst-case scenario becomes practically infeasible to even consider. And it's not just OSes that don't particularly care about real-time - modern processors don't either. e.g., in the common scenarios it's possible to load maybe eight 8-byte values per nanosecond (maybe eight 32-byte values if you're doing SIMD), but…
I feel like this comment is from an alternate reality where the Windows lock screen doesn't just drop all your inputs for a random period of at least a few seconds when you try to enter your password.
Yes, the screen still locks, it just doesn't eat your keystrokes anymore. If you have Windows Home edition without gpedit.msc there's a registry key you can set instead, you'll have to google it.