I think the real space saver is not necessarily "hexadecimal system" per se but the "bitmapped graphics" technique that they seem to be referring to. Nowadays, graphics information doesn't tend to be packed in bitmaps, either manually or otherwise. It's pretty inconvenient for processing to have everything bitmapped (compositing, collision detection, etc.) and they probably wouldn't do it if it weren't for the space savings
Yes you are correct. Take something like the Super Nintendo, it typically displayed hundreds of colors on screen, however each graphical element could have a maximum of 16 colors (4 bits).
The way they solved this was by having CLUTs (color lookup tables), so for the Super Nintendo (if my memory serves me) you had 16 different CLUTs that you could assign to a graphical object, each able to contain 16 unique colors.
This is what made something like the Super Nintendo graphics look so much better than say the Amiga 500, both used bitmap graphics, but the Amiga did not have a CLUT solution, so you were stuck with 32 colors except for more advanced graphic modes which weren't really usable for games.
In the US, how many current animated shows can you name? I can name a decent fraction of cartoons from the late 90s, but am completely unable to name anything since then--at least until I got a nephew and am now getting acquainted with the relevant demographic shows. That's a 20 year gap in shows.
Compare other media. How many classical composers can you name? I doubt many people, even erudite people, could push well beyond the basic frontier of Bach, Beethoven, and Mozart. Recognition of well-known tunes (such as Pachelbel's Canon, whose name my spellchecker doesn't appear to recognize) is going to far exceed their name, let alone the composer's name.
The most recognizable anime to a layperson in Japan is likely to be the big mega-blockbusters of various eras. I'd be more shocked if you said that no one had heard of Mobile Suit Gundam, Dragonball, Naruto, or Attack on Titan [which one they'd pick up on depends on their age] than any of the shows you've mentioned. Hell, the only thing you listed that I'd think people in the US with a passing familiarity with anime might know would be Cowboy Bebop.
But it seems very popular, out of the top ten highest grossing films in Japan, 5 are anime (Spirited Away, Demon Slayer, Your Name, Princess Mononoke, Howl's Moving Castle), and the top two are Spirited Away and Demon Slayer.
In North America's top ten you will only find one animated feature, Incredibles 2, and it is at position ten.