It's generally considered a fact that Linux, along with many other open-source software projects, are more efficient than their propriety closed-source counterparts
This is not necessarily true. Linux had trouble with Nvidia Optimus, which is a GPU technology that seamlessly switches between power modes. Well, that is if it works properly, which it didn’t for Linux. I haven’t heard it in a while, so I assume it’s not a problem now anymore.
But it was a big problem where Linux laptops drained batteries much faster because they were using the GPUs at max capacity at all times.
What I’m saying is that the efficiency of Linux depends on access to hardware features, and that might depend on the vendors of the drivers.
Also, like it or not, if there’s one thing I envy about Mac is its power efficiency. They usually last really long on one charge.