jj's template and revset languages are very simple syntactically, so once you're comfortable with the few things you do use often it's just a question of learning about the other existing functions (even if only enough to know to look them up), which slot right in and compose well with everything else you know (unlike flags which typically have each their own system).

Or, perhaps better yet, defining your own functions/helpers as you go for things you might care about, which, by virtue of having been named you, are much easier to remember (and still compose nicely).