I don't find that particularly credible. If Microsoft would boot all security products (including their own) out of the kernel and force them to use specific in

I don't find that particularly credible. If Microsoft would boot all security products (including their own) out of the kernel and force them to use specific interfaces for this there is no anti-trust concern at all there. It would only be a problem if they wanted Windows Defender to remain having privileged access while taking it away from everyone else.