Whatever protection is implemented in user-land can be removed from user-land too. This is why most EDR vendors are now gradually relying on kernel based mechanisms rather than doing stuff like injecting their DLL in a process, hooking syscalls, etc...
First, we were talking about EDR in Windows usermode.
Second, still, that doesn't change anything. You can make your malware jmp to anywhere so that the syscall actually comes from an authorized page.
In fact, in windows environment, this is actively done ("indirect syscalls"), because indeed, having a random executable directly calling syscalls is a clear indicator that something is malicious. So they take a detour and have a legitimate piece of code (in ntdll) do the syscall for them.
