That’s… all stow does, there’s nothing more to it. If you need some other feature don’t waste your time trying to make it work with stow, It’s just a meme in my opinion.
About the “package manager” functionality, stow was originally supposed to be a development tool for the Perl programming language, you download a bunch of libraries into a directory, then use stow to merge those files into the root of your project (like a caveman), as it turned out some people started using it to manage dotfiles, and here we are.
When I started trying to organize my dotfiles, I started with stow, but quickly found it very limited.
After that I found dotdrop, which is considerably more involved, but gives you total control. My config with dotdrop quickly started growing insanely huge, at some point I even had system-wide systemd services declared.
Then I found out I was basically reinventing nixos and home-manager, so I switched to that.
chsh does not modify /bin/sh
Maybe you’re thinking of a certain video from a certain YouTuber who linked /bin/sh to fish?