I think what is meant is that the list is the primary data structure for everything in lisps. Fortunately, it is not the only data structure in lisps. I dislike constructs where eg. a graph edge is built as:

'(GRAPH-EDGE <source-vertex> <target-vertex>)

whereas in ML you would write

type edge = { source: Vertex.t; target: Vertex.t }

which is not a list, but an entirely different representation. In Common Lisp the representation could of course be a CLOS object or a DEFSTRUCT (I think, my CL-fu is definitely not that good).

As for the composition, lisps are lacking (nice) currying which is one of the basic building blocks when constructing combinator-libraries.