I'm not sure anyone is saying it performs better. Some people demand multi grained, lightweight stunners. Due to the nature of how willow is grown and processed now, we're told these are rarer to come by. So, this creates that new grade really. It's a bit of both, customer driven and then brand/supply driven to meet demand. If people didn't want them, or demand them, it wouldn't exist and those people will generally be happy to pay more to get what they want. Fair play to you mate if you don't follow that model, but there's more to it imo than your making out here from a business perspective.
On the flip side. Do batmakers get to claim back for storm damaged clefts, clefts where bark excursion, big knots aren't apparent? No, they take the hit. In the grand scheme of things I've seen happen in the industry, creating a top tier of willow for potentially the 1 to 2% of willow you get isn't a crime imo.
Things change. If and when things become harder to get a hold of, then they become more exclusive and they're expensive. If you sold a 20 grain perfect looking cleft as a G1, how would the next customer react when you sold them a 7 Grainger with a bit of spec as a G1 and charged the same? It's probably why GM have about 14 grades essentially, as 3 or 4 probably don't really cover it anymore.