I like bash, it's very standard. If you need better autocomplete I'd absolutely recommend ble.sh, which gives you an experience more similar to fish, without having to relearn the entire shell.
Look, I've been a fish user for years and still use it on some machines, but there are always cases where I cannot install fish, or fish is incompatible with a program I use (even via bass) or a feature I use in bash scripting works differently. Of course, I can always fix it, but it's always faster to just drop into a bash shell. I'm also much more familiar with configuring bash than zsh and therefore that's what I use. That's why bash is a staple on all my systems, even my BSD machines.
I think different shells are interesting and provide unique takes on what a shell can do, but telling people to stop using something that's so ubiquitous and useful to learn comes off as grandstanding to me.