Anything bad that can happen with a kernel anti-cheat, can effectively happen with a user-mode one as well.
It’s definitive FUD spread around.
You don’t need kernel address space permissions to access a user directory full of sensitive information, just enough permissions a normal app like a game would have already.
If you do NOT want that to happen, then ask developers to implement their applications inside a sandbox.
It’s unfortunate that WinRT didn’t fully supersede Win32, as WinRT was designed to be a properly sandboxed experience.