India isn't really missing so much as not distinguished, but also that.
Every island is missing, starting by size with Greenland.
Northern Canada is pointed instead of concave with Hudson's Bay. Antarctica is also missing but that counts more as a stylistic choice because it's so frequently done.
What you'd do is, you pick a representative set of points from a world map, e.g. by reducing it to a low resolution, or by sampling with blue noise. Each point gets a 32-bit integer. For up to 32 circles, you check if each point is inside or outside the circle, and mark one bit accordingly. Every region created by these overlapping circles now has a unique ID for all points inside that region.
Scoring groups points by ID, finds whether each group contains more land or water points, and counts all the points outside that majority. That sum is your error.
I love this. I'm guessing there's a better way to choose circles, though.
Why have one for the Great Australian Bight? Just so it doesn't end up being an entire circle? That's kind of a missed opportunity to do a Philippine Sea circle and include SEA.
Edit: What about one for each continent, a couple for the Indian ocean, and then a big Pacific Ocean one that takes out of Australia, East Asia (forming SEA) and the two in America?