There is overlap with some of the most fundamental characters, notably alcohol levels and hop bitterness. So why are there separate style categories for these two beers that on the surface resemble barley wines?So, Double IPA = green barleywine, so sayeth the high priest (I really want to call him the Pope, but I don't want to offend any Catholics out there). I couldn't make a better case that there are too damn many styles.
Neither the barley wine ales nor the double India pale ale and imperial or double red ale descriptions make a point that barley wines are primarily intended to be aged. Double India pale ale and imperial or double red ales are designed to have a bright hop character that is fresh and assertive. These beers are not stylistically intended to be aged. The brewer’s intention is to present a fresh, bright and lively beer to the beer drinker.
(My vote: you have a single category for stong ales into which you dump all the double and imperialed beers--stout excepted. You have your IPA, your strong ales, your barleywine. Done.)