Cofty I agree.
As far as what was identified by re'em, it's as uncertain and speculative as many other colloquial names for animals, places and expressions. It's entirely possible it meant different things to different authors, even taking on a mythological element in some contexts. What we can be sure of is that a 5th or 6th century BC author was not referring to a long extinct creature. Jewish scholarship has generally favored identifying the animal as the much more recently extinct auroch. A large wild bovine that did in fact exist in parts of the Middle East. It is likely this was the animal by which El and later YHWH were symbolized. Indeed, YHWH is described as having the horns of the re'em.
17 In majesty he is like a firstborn bull; his horns are the horns of a re'em.
Rather ironically the wild auroch while seemingly untamable was in fact the animal from which we get domestic cattle.