ok, I read it in a different direction
For that more strict scenario, have a read at this blog post [1] written by a lxc/lxd developer - basically it resumes the efforts to have “lxc-exec” as a solid alternative to “ssh”, including highlights of the differences and challenges involved.
On the other hand, personally I see the “ssh” as a more extended/standars “interface” for management, which enables for example the coupling with other tools - like “Ansible”, to automate the deployment and configuration of new containers (beware the ansible module for lxc/lxd was outdated last time I checked…)
[1] https://cbrauner.wordpress.com/2017/01/20/lxc-exec-vs-ssh/