I found that definition, applied liberally, lost its effectiveness.
I've never found the use of parenthesis to be an inhibiting factor in the complexity of Lisp code. It's a piece of syntax that has a single use and isn't ever over-loaded. A parameter list... is a list. A form... is a list with a specific structure. Surprise. The hyper-spec is very clear on this (i.e.: there is no over-loading).
I don't think his justification for [] was really necessary. If you want a different syntax for the defun macro you're free to have at it in Lisp. Clojure did nothing special there. Most schemes could interchange braces if you wanted to. You could easily write your own defn macro with your preferred syntax. It is no great innovation to use a different syntax so I don't know why he bothered making that remark about Lisp.
I've never found the use of parenthesis to be an inhibiting factor in the complexity of Lisp code. It's a piece of syntax that has a single use and isn't ever over-loaded. A parameter list... is a list. A form... is a list with a specific structure. Surprise. The hyper-spec is very clear on this (i.e.: there is no over-loading).
I don't think his justification for [] was really necessary. If you want a different syntax for the defun macro you're free to have at it in Lisp. Clojure did nothing special there. Most schemes could interchange braces if you wanted to. You could easily write your own defn macro with your preferred syntax. It is no great innovation to use a different syntax so I don't know why he bothered making that remark about Lisp.