I believe the concern at hand is more a discussion of total screen real estate, vs uninterrupted screen real estate. Total screen space did indeed increase with the island, whereas uninterrupted screen space actually decreased, due to the bottom edge of the island being positioned lower than the bottom edge of the notch. Each use case has its value, and Apple chose to prioritize total instead of uninterrupted.
It is indeed a marketing trick, of a sort... but not just because a dead pixel zone still exists. It's also something that they can use as a differentiator between models, and it's something that they can -- in select circumstances -- make less obvious through the use of accessory graphics surrounding the island, such as when they display the login face in the black square; they actually use the unavoidable negative space of the island as part of the desirable negative space surrounding the icon. It's actually kind'a brilliant, in its own way.