You have taken this discussion to unrelated security and data center issues that have got nothing to do with the topic on hand. You dwell on the security of seccomp, selinux and apparmor that have nothing to do with libvirt specifically.
I am not interested in discussing libvirt, virsh or virt-manager and its various offshoots. And given libvirt is the what virsh and virt-manager use in the context it's disingenuous pedantry to make a distinction.
I am interested in understanding how kvm can be made more accessible to virtualbox users. If that's not something that concerns you and you would rather dwell on defending libvirt then that's not a productive discussion. If libvirt was the solution we would not be having this discussion to start with.
And you seem to be comparing Virtual Box with libvirt, which is equivalent to comparing apples to aardvarks (okay, that's an exaggeration). But seriously, a fairer comparison would be Virtual Box vs. Virt-Manager on Linux.
Here, I admit -- I'm not a daily Virt-Manager user (I live on the command-line), so I can't tell you where exactly it is lacking compared to Virtual Box.
If you've tried it, & have suggestions​, you might want to write to:
https://www.redhat.com/mailman/listinfo/virt-tools-list
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About the libvirt's internal representation (in XML -- yes, I'm not a big fan of it either, and I suspect, nor are the current maintainers; had it been today, they would've likely chosen a more gentler-on-the-eye format like JSON or some such) of guest definition: Most users don't need to touch the XML definition at all. Most tasks that are involved in managing VMs can all be done trivially via Virt-Manager GUI, or the command-line, virsh.
And the regular libvirt configuration files are all in standard Linux configuration file format.
> Are you saying selinux, apparmor and seccomp cannot be used on qemu processes without libvirt?
No, I'm not saying that. My argument (based on daily interactions with users on public IRC & mailing lists) is that, for QEMU-based guests, libvirt makes it easier.