Regarding your first point, why not just run scripts with `bash script.sh` or even better, use shebangs and `./script.sh`?
The standard shell experience is decades old, and makes it cumbersome to keep up with the pace of today. The appeal of zsh/fish is the user experience and extensibility. I have a shell config using zinit [^1] that installs my dev environment for me (fzf, tmux, nvim, and my zsh-plugins) as long as zsh exists on the new machine. While one may argue that they prefer strictly standard bash so that everything is POSIX compliant, you just have to ensure that your scripts are run with bash or whatever shell the script was made for.