I think Elvish's simple completer API (which is very similar to completion protocols used by editors, FWIW) is proof that serious programming capabilities is actually quite essential for a shell. You wouldn't write editor plugins using bash, but people have to write completers and other shell plugins in bash all the time.
However, what would affect your day to day experience the most is probably the coverage of existing completers. There are some community efforts you can find in https://github.com/elves/awesome-elvish#completion-scripts, but it's quite clear that Elvish is lagging behind.
This is mostly because I'm still trying to figure out a lot of things in the language itself, and I don't want people to invest a lot of completers before they get broken by language changes. Once the language becomes more stable (which will perhaps take another year or so) I'll invest much more in this area.
I don't know if you have tried it but fish basically predicts what you are going to enter based on the directory you are in and what you have entered before and gives a preview as you are typing, and then you can hit the right arrow to complete it.
Since that is extremely convenient for me and your shell seems to not have color (at least not in my Ubuntu terminal right now), I am going to stick with fish.
clap-rs, which is a popular command line parser for Rust, can generate Elvish completion scripts automatically and it works really well. Maybe you want to add that to the list.