Mac OS switched to zsh a couple releases ago due to bash being GPL 3 so the shell isn’t old anymore and installing bash is as easy as brew install bash.
The default OS-provided shell is irrelevant; anyone who cares an iota about DX on their dev machine is going to set up their terminal and shell from scratch anyway.
Unfortunately it's also a headache to use Linuxbrew with RHEL because it keeps trying to install its bottled glibc which doesn't like the old (but heavily patched) kernel and breaks everything not statically linked to the system libc until you remove it.