Storefront retail in prosperous urban areas is far from in decline. If it were in decline, rents would be falling; actually, rents are surging.
Big boxes in the suburbs? Yeah, they're in decline. But not in urban neighborhoods.
Your causation is off. Rents in urban areas are soaring not because of prosperous times for retail/restaurants, but rather because land values have skyrocketed and the landlords either need to make up the difference or are just plain greedy.