It's not the prefix-system per-se, but it is the fact that code and data are sufficiently similar that you don't have to context-switch when writing macros is very nice.
Your argument seems to be that Macros ought to be harder to write in exchange for being easier to use? What non-lisp macros are easier to use than lisp macros, and how?
I think his argument is actually that the extreme simplicity of defining a macro in CL hides the fact that writing correct macro code isn't very simple. Using gensyms to create bindings in macros is an example - it's not obvious, but often critical for getting macros to behave nicely. Things like accidently capturing variables, multiple evaluation, etc. make "real world" macros difficult to write. Not insurmountable, of course, but more difficult than just basic list processing.
Ideally that has no impact on how easy it is to use a macro, except to the extent a bug would make the macro hard to use.
Your argument seems to be that Macros ought to be harder to write in exchange for being easier to use? What non-lisp macros are easier to use than lisp macros, and how?