It's a mistake to ignore the customer

Not quite. The problem, in a sense, is that the structure chosen for representing program makes sense for optimizing interpreter a bit, at the cost of being very unnatural. Subtrees are not subexpressions. Sure, that way you avoid digging in to find the node where you'll be doing reduction, but that doesn't come for free. As the matter of fact (and you damn well know that, seeing that you seem to be familiar with e.g. Haskell), the things can be done the other way round - with APPLY being the fundamental primitive and CONS expressed via it. The same "easily represent program in the language's primary data structure" thing holds for a lot more than just LISP, e.g. when the primary data structure *is* partially evaluated expression. That's not what makes LISP LISP; neither is the syntax, of course.