This is accurate as far as page protection goes. The problem is the largest threat model.

If Process A and Process B are running in the same user context on a desktop OS, PAGE_NOACCESS is not a strong boundary by itself. Process B may be able to obtain PROCESS_VM_OPERATION/PROCESS_VM_READ, change the page protection with VirtualProtectEx, inject code that calls VirtualProtect inside Process A, load a DLL, attach as a debugger, duplicate useful handles, or tamper with the executable. That's the problem with same-user process isolation, it is a hugely leaky abstraction. There is no magical "just set this bit" fix.

On a desktop OS, once an evil process runs under the same user context, you are relying on process DACLs, integrity levels, code-signing, anti-injection hardening, and file-system protections. You can plug one path and still have several others.