[londons_explore]

The data before packing and the data after unpacking are probably not the same formats.

Some of the packing steps are also probably lossy (eg. Take this super high poly count model, and cut away 99% of the polygons). If you skip that culling step, the game probably won't run.

[gambiting]

Yes, that's exactly what it is. The "data" might be 8K textures, as part of the binarization it gets converted into a format that the client can understand, but also follows a "recipe" for the texture set throught the editor(so convert it a 2K texture with a specific colour spec). Same for models etc.

And yes, the client itself usually can't read the raw data, and even if it could there is not enough ram on consoles to load everything as-is. The workstations we use for development all have 128GB of ram just so you can load the map and all models in-editor.