> And how useful is all that in practical real world use cases compared to Android or Linux
There are several possible answers.
1. It's something like 1% of the size and originally ran on systems with circa 4MB of RAM, booting and executing from ROM. There is a lot of value in code that is small enough to study and understand. Modern Linux is incomprehensibly vast and complex:
https://micronews.debian.org/2023/1686455026.html
1.3 billion lines of code. No human can live long enough to read and understand that.
2. Diversity is good. Monocultures are bad, because they are extremely prone to exploitation and attack. Find an attack that gets at a system at a low level and everthing based on that system is vulnerable.
Combine this fact with OSes of vast size, in non-memory-safe languages such as C, and the result is a multi-billion-dollar industry of constant security fixes and the need for high-bandwidth connections simply to download the constant stream of updates.
3. This is not some academic unfinished plaything. It's a former industry-standard OS that shipped on millions of consumer devices and had an entire ecosystem of apps and tools. IMHO that makes it more valuable than, say, Genode or something.
4. This may just be me but if rich modern tools are themselves of vast size and complexity, then that makes them inherently of lower quality compared to smaller simpler tools that can do the same job.
VS Code is built in Electron:
https://www.reddit.com/r/vscode/comments/mwsejl/why_vscode_i...
Electron is built on Chrome:
https://www.electronjs.org/
Chromium itself is incomprehensibly vast, nearing 35 million lines of code in over 40 different languages:
https://openhub.net/p/chrome/analyses/latest/languages_summa...
Never mind what it can do -- I think you simply can't trust something that big.