Since I can't edit my post anymore, here are some additional thoughts:

Traditional shell scripting languages are great at exactly three things: typing commands interactively, running other programs, and sourcing other shell scripts. They are also is distinct in that they are "stringly-typed" (i.e. everything is a string), and moreover that syntactically bare symbols are also strings.

Typing commands interactively is essential because... it's a shell. That's what it's for. Most programming languages do not and should not optimize for this. But it's literally the purpose of a shell, so a shell should be good at it.

"Running other programs" includes invoking them (literally 0 extra syntax), piping them (one letter: |), and redirecting the standard input and output streams to files (>, <, <<, etc.). This is one of the great innovations of Unix and nothing holds a candle to its elegance and convenience, even if sometimes we get frustrated that pipes are "dumb" streams of bytes and not something more structured.

"Sourcing other shell scripts" practically isn't much different from "running another shell process", except that source'd shell scripts can set shell parameters and environment variables, which is an important part of e.g. the X11 startup system: the global /etc/X11/Xsession script sources the user's ~/.xsession script, so any environment variables set in the latter are propagated to the former, and thereby are inherited by the X11 window manager when it eventually starts. If you wrote the /etc/X11/Xsession script in any other programming language, you'd have to inspect the environment variables of the ~/.xsession process and "merge" those values back into the current process' environment.

On being stringly-typed, I think it's mostly good in the context of the "two things that it's good at" described above. It cuts down on syntactical noise (otherwise "everything" "would" "always" "be" "quoted" "everywhere"), makes string interpolation painless, and generally supports the "typing commands interactively" use case. Make and Tcl are the only other popular languages in this category. Perl and Ruby allow it in specially-delineated areas of code. Moreover, Bash, Ksh, and Zsh all have arrays, which helps fix some of the biggest problems of everything being a string.

In short, if your program can make good use of the above features, then a traditional shell is a great choice. If you program does not need those features, do not write your program using a shell script, because shell languages are awkward at best in pretty much all areas.

And if you are considering an "alt" or "neo" shell language, in my opinion it must excel in the above two categories. Being stringly-typed is a matter of taste, but the language should also probably support bare-symbols-as-strings and string interpolation.

Python, for example, is not a good shell scripting language because it is not easy to type nontrivial commands interactively, it lacks tidy syntax for input/output redirection (even though it's actually pretty easy using the standard library), and it lacks bare-symbols-as-strings. So instead of:

#!/bin/sh
foo -x 1 -y 2 "$ABC" | bar --json -

you have to write something like:

#!/usr/bin/env python3
import os
from subprocess import Popen, PIPE, run

foo_cmd = ['foo', '-x', '1', '-y', '2', os.environ['ABC']]
bar_cmd = ['bar', '--json', '-']
with Popen(foo_cmd, stdout=PIPE) as foo_proc:
foo_proc.stdin.close()
run(bar_cmd, stdin=foo_proc.stdout)

You can of course write your own library that abstracts this and uses symbols like > >> < << | to mimic what a shell does. Maybe that's what Xonsh is, I haven't looked at it myself. But this hopefully demonstrates why the base language Python is not a good shell, despite it being portable, being nearly ubiquitous nowadays, being relatively easy to use and learn, being "safe" in many ways that traditional shell languages are not, and having a huge and useful standard library.