It should be pointed out that no elementary spin-zero particles have ever been found. In fact, the ad hoc introduction of these is considered by many theorists to be an unpleasant feature of the standard model.

Well, heck! Standard models are always loaded with unpleasant features, aren't they? If you want pleasant features you have to pay more money and get the deluxe model. Doesn't matter whether its a GUT or a SUV, the same principle applies.