Pretty similar to #280 - end gateways are basically a full opaque cube, so it'd be expected that they'd cull against each other, but that does not happen.

They don't cull solid blocks next to themselves either, though I'm not sure if that's desirable or not:

Leaves don't either, and I'm not sure if that's intended:

End Gateways are weird and I don't think there's any point in trying to optimize a block that only appears very rarely.