Academically but probably not practically interesting
These studies always have an interesting academic angle (although in this case the results seem a little obvious), however the details never take into consideration the bigger picture.
I'm unlikely, for example to be able to fully max out multiple bare-metal Linux servers to the same efficient degree I can running containers. Dedicating hardware resources creates fragmentation that results in the loss of any savings. Just think of how workload demand curves change over the course of a single day for any given application.
Then there are questions on poorly written code, or even more efficient code that works better as a microservice than monolithic application. What about patching and maintenance? What about backup (backing up a stateful bare metal server may consume more resources than never backing up a stateless Docker host).
As I said, interesting academically with little practical use.