[axiolite]

I find most of shellcheck's opinions quite arbitrary.

Wider shell compatibility is a good reason to use backticks. Avoiding nesting is always possible. Quoting may be a concern in more complex usage. But yes, I know well, and often also use $( ) syntax.

Making a lot of noise about use of (the shellcheck author's) non-preferred syntax, which works perfectly fine in a given context, is a design flaw that renders shellcheck useless to me. I'm perfectly capable of finding an opinionated pedant on my own who will also critize the syntax I use (with little or no justification), and offer no actual help...