I find square brackets quite useful for some kinds of expressions, that have multiple cases or branches. To make a visual difference there can help with readability.
I also find square brackets useful for other kinds of expressions, like Python-style list comprehensions. Though such syntax predates Python, e.g. there's a paper from 1991 https://3e8.org/pub/scheme/doc/lisp-pointers/v4i2/p16-lapalm... whose code still works in Common Lisp. If the language doesn't mandate that square brackets mean something, as Clojure does, then I can make them mean what I want that is convenient for my namespace, as Common Lisp allows. Whether that's data literals or special syntax or something like [x (x <- xs) (oddp x)] to filter out odds, it's nice to have that choice.
I use rainbow delimiters (colourful brackets) for that, but I can accept square brackets as an alternative for people who have issues with colour perception.
Most complaints against lisp predate all of the currently in use editors, though? More, it used to be a bit of the norm that everyone had their own editors. Dr Racket being in that vein.
Such that, sure, emacs can feel awkward. But the Arduino editor isn't exactly smooth. And my kids picked that up ok.
And a big plus on common lisp is that the older texts all still work.