Linux

Doesn’t the shebang at the top of a bash script negate that compatibility issue anyway?

Yes. Fish is equal to ZSH when running scripts. But has more trouble if you are writing scripts you want other people to run (this is quite rare these days though, maybe just use a proper programming language if you want to write/share software).

Fish is worth trying out! I have used both fish and ZSH both for around a year. Fish is a better experience overall. You don't have to maintain a bunch of config files for the same level of features and it is generally faster.