The parent is almost certainly referring to the distinction between:

(-> (initial) a b c d e)

and

(e (d (c (b (a (initial))))))

I find -> and ->> useful, but the new threading operators kind of silly; they're very easy to implement in terms of -> and ->>, or in terms of higher-order functions, and don't really cover all the use cases one would want---it offends my sense of aesthetics to have them (in their particular implementation) added to the core ns.