This very much confused me as well. I went to export my images, and expect the 'Nearest Neighbour' to apply this on export to everything so I have no anti-aliasing in the final output. It's unintuitive to have to apply this to a per-layer basis within my document. This is something I want to change how the vector lines map on export for the document I'm creating at that time and select my different filtering options. Nearest Neighbour should provide me with the option for no aliasing, that's how it's documented in the help:
I expect this setting in the export dialogue to make a visible change, from what I can see, any of the settings effectively do the same thing and are indistinguishable... so what's the point then?
See this with both PNG and WEBP formats. This wasted I don't know how much of my time, and required me to find this post with the link to the blend options, no way I would have associated that or discovered that otherwise. It's part of the export process, there's a setting there, it's what's intuitive and expected of the setting, and is documented for that purpose. It should perform that operation.