That does not apply to texture files where the textures are directly memory mapped (as opposed to all being read on block by block). This both simplifies game design and speeds things up.
Also, decompression speed depends on which algorithm you picked. Most of the fast-decompress algorithms are not good at compressing raw pictures (textures) or raw audio.
And the most modern NVMe are very fast, probably faster than what you can get out of a compression algorithm that is good for textures.
Finally, you can turn on compression in your filesystem if you really want to load CM from a compressed storage.