> This great idea of Lisp (the simple syntax of function calls in round brackets) isn't much different than a good macro assembler even back in the 1960's.

Far from it. Recursive functions and symbolic expressions were nothing like assembler back then.

> You can indent a Lisp program in any way but the language doesn't require any at all.

One can indent it in any way, but practically people use common indentation styles. Lisp also provides formatting&indentation via the pretty printer.

    CL-USER 48 > '(DEFUN COLLAPSE (L)  (COND 
    ((ATOM L) (CONS L NIL))
    ((NULL (CDR L))
    (COND ((ATOM (CAR L)) L)
    (T (COLLAPSE (CAR L))))) (T
    (APPEND (COLLAPSE (CAR L))
    (COLLAPSE (CDR L))))))


    (DEFUN COLLAPSE (L)
      (COND ((ATOM L) (CONS L NIL))
            ((NULL (CDR L))
             (COND ((ATOM (CAR L)) L) (T (COLLAPSE (CAR L)))))
            (T (APPEND (COLLAPSE (CAR L)) (COLLAPSE (CDR L))))))

> I think with practice, some programmers developed an eye for the lack of structural clues

Lisp has a lot of syntax and structural clues, but you just don't know them. You have to learn them, since much of, say, C syntax knowledge does not carry over to Lisp.

>and made some reasonable size code.

Like the 1 million lines of Lisp code of the Lisp Machine OS? Or the several hundred thousand lines of an editor largely written in Lisp (GNU Emacs)?

> Linked lists are poorly executed in modern computers that rely heavily on locality of data

Lisp nowadays usually does not execute linked lists, but runs compiled Lisp. Some data is in linked lists, but there are many other data structures not made of linked lists. Still the language runtime is often pointer heavy.