You are correct; I confused archiving with compression. However, even considering only the compression process, same compression parameters cannot be guaranteed, as it is unknown which compression parameters the image publisher used.

Thats true. And regardless of compressed vs regular tar, I think the OCI format working with opaque archives is extremely limiting. I hope the industry will eventually redesign to use content addressable storage per file and have metadata to describe the layer/disk layout instead. That would allow per file deduplication, and we can use tar for just bulk transfer over the wire, rather than using tar for the data at rest.