Nothing keeps you from following the FHS inside your container or sandbox.
Are you referring to the location where container images live? Then `/var/lib/containers/` and `/var/lib/containers/storage/` would be perfectly FHS compliant.
Systemd frustrates and angers people with Poettering's complete disregard for bug reports, tradition, and basic common courtesy. At the same time, change needed to happen and change is gonna hurt. And big changes can't wait until they're just as stable as the old system: does anyone develop software like that in their own careers? I try not to ship complete crap but "just as stable as v1" is never a goal.
Poettering is a Microsoft employee. It is normal that he follows the direction of the mothership. What is not normal is, that he has so many blind followers.