That would be true for FASTA compression but FASTQ files contain other data. With a MiSeq, for example, 1/3 of the data is the DNA sequences, 1/3 is a quality s

That would be true for FASTA compression but FASTQ files contain other data. With a MiSeq, for example, 1/3 of the data is the DNA sequences, 1/3 is a quality score (0-37) and 1/3 is a header which includes things like flow cell ID but also a lot of info on the physical registration address of the cluster on the flow cell. In some applications this info is not required, but is from a scientific/data integrity perspective