What is referred to today as "Linux" is an operating system that has a lot more components than just a kernel.
Yes, yes, and the "computer" is the thing that sits on your desk that displays stuff while the "hard drive" is the beige box on the floor.
Don't mistake a technical term for lazy incorrect usage by people who do not know what they are talking about.
"Linux" is the kernel. "RedHat Linux" is a distro that uses the linux kernel. Lazy people call the entire stack linux. Android is a very different approach that also uses the linux kernel.
there are certain kernel features required by systemd
However you do not need SystemD to run those kernels which seems to be what you and the other poster are implying.
SystemD is Lennart's special little empire building project and separate to the kernel.
If they were going to optimal cost efficiency
In that special case saving on weight is optimal cost efficiency. I doubt that any of the rover components cost as much as their percentage of the total weight divided by the cost to get the rover on Mars.
It's getting pretty difficult to think that there aren't a lot of people here who do hate America
Some of the press is focused on that and blowing it out of proportion.
Remember that even Bin Laden hated some people supported by US government military aid far more than he hated the USA.
You will be successful in your work.