Was he? Possibly at one stage, but he only signed for £6-7 mill or so, a relatively modest fee for what was supposedly one of the most promising centre backs in the world at the time.
The fact that Zabaleta was an Argentine international doesn't automatically make him some obvious buy either - Jonas was an international when we signed him and only a handful on here had any idea of how good he was iirc.
Not denying that Hughes signed plenty of dross at Man City and QPR when given what was effectively financial carte blanche in either case, but on a budget he's a pretty shrewd operator I'd say.