I was bored at work the other night and ran some numbers:
4096 x 2160 letterboxed to 21:9 wastes only 19% of the available pixels.
3480 x 2160 letterboxed to 21:9 jumps the wast to 24% of the pixels you paid to get
1/5 or 1/4 (close enough for comparison) of pixels tossed down the oubliette of the aspect ratio inquisition.
Movie theaters have always been letterboxed by curtain adjustments to cover the unused sides of the screen. The unwashed masses never noticed that, now the want the full screen experience they've been used to before big (wide) screen TV and ubiquity of full screen content at long last.
4096 x 2160 letterboxed to 21:9 wastes only 19% of the available pixels.
3480 x 2160 letterboxed to 21:9 jumps the wast to 24% of the pixels you paid to get
1/5 or 1/4 (close enough for comparison) of pixels tossed down the oubliette of the aspect ratio inquisition.
Movie theaters have always been letterboxed by curtain adjustments to cover the unused sides of the screen. The unwashed masses never noticed that, now the want the full screen experience they've been used to before big (wide) screen TV and ubiquity of full screen content at long last.