I'm not sure which of the parent posters started but it seems like we're conflating two rather unrelated meanings of the word "compression" here: compression in

I'm not sure which of the parent posters started but it seems like we're conflating two rather unrelated meanings of the word "compression" here: compression in the sense of data-compression (which is often lossy for many audio formats like mp3) and compression in the sense of dynamics-compression, which is what is meant by "compression" in the context of mastering.