I don't have any answers, just my own experiences. Last year I decided to use Alpine Linux as my Operating System for a couple of self-hosted things running on a Raspberry Pi. I chose it because it's super minimal and used less common tools (for example doas instead of sudo). That unintentionally forced me to learn how to use Linux using more basic commands that are more likely to be available on other Linux systems.

Alpine Linux uses Busybox-Ash which is a POSIX compliant shell that's very small and very basic. The scripts I ended up writing tend to be POSIX portable meaning that they should work on a wider variety of systems. That comes at the cost of script simplicity and readability as well as missing out on many features that make Bash scripts more complex, robust and easier to work with.

I have a working example POSIX portable script. I've been adding to it all the things I've learned. You can check it out here if you're interested.

I use Alpine Linux with Sway as my daily driver but still keep a copy of Linux Mint DE ready to use because it's nice to have a fully featured work environment for the days I don't want to think.

You do not want to use dash interactively! It is created solely for scripting and not for creature comfort. This means all the stuff you're probably used to such as line editing and command history will not be available.

At some point, you'd want to ask yourself how heavy is "heavy" and how much stuff are you willing to shed? Do you not need tools such as web browser, media player, or office suite? Are you willing to get rid of desktop environment?

In the extreme, you can remove all the documentations, all the manpages to save space. You can even remove all the localization files, without which stuff would look weird, but would still run.

Further than that, you can even customize your kernel, opting out all the drivers you don't need, or even some that you could use (e.g. wifi, audio, hardware monitoring). Next, some kernel features that are less essential such as statistics, logging, and debugging, as well as the handling for some network protocols. If you wanna go crazy, you can enable the expert/embedded options and with that you can disable stuff that can be critical (e.g. error reporting, certain IPC feature).

It's a rabbit hole, really.

I do write my scripts in POSIX sh, more for compatibility sake. But shells like dash, mksh, are not made for interactive use, they lack most not-really-convenience features.
But heavy, that's only invocation time; it mathers more if you do things like 100 awk calls (that one is heavy to invoke) per line you parse.

Though i did write my own cross-shell session scripts, centering on the ENV variable which most shells understand (and a /etc/bash/bashrc loading it, since Bash doesn't).
Again, more because i think, why load xkb maps 3 times in 3 scripts if you can do it only once? And most session scripts look like they were never touched the last 20 years. And then a if you do it, do it right mindset.

Worth learning; i think so. You learn, with time, more about how to use shorthands and functions, to structure your scripts nicely, instead of doing if if if messes more "convenient" shells lead you to. Which benefits you in real programming languages too and leads to more readable and better maintainable scripts.
And the only times i miss convenience features like arrays is in 500+ loc scripts which would have better been done in python.
Btw, don't do 500+ loc shell scripts: they do become a maintenance mess even if you do everything right.

Edit: right, i forgot the POSIXLY_CORRECT env variable. Some AUR setup-scripts have issues with a forced POSIX shell.