> The ones that stand out the most are the autocomplete (for example,
> autocomplete for umount only shows mounted devices),
autocomplete behaviour is not really built-in or more exactly the built-in default behaviour is not suitable for many commands, e.g. umount. Bash does offer an API for everybody (i. e. every command) to get customized autocomplete behaviour.
I have always wondered why there are so many commands that do not install suitable autocompletion scripts for bash. But hey, it's open source. Maybe we should comment less and code more... Contributing those scripts might be more laborous than writing them, though. They don't just belong to bash but you have to work with every command's upstream.