I think you're looking at a different perspective than me. At _build time_ you need to process O(n), yes, and generate O(n) additional data. But I said "The amount of data you need to decompress is a constant". At _read time_, you need to do exactly three steps:

1. Load the file index - this one scales with the number of files unless you do something else smart and get it down to O(log(n)). This gives you an offset into the file. *That same offset/32 is an offset into your gzip index.*

2. take that offset, load 32kB into memory (constant - does not change by number of files, total size, or anything else apart from the actual file you are looking at)

3. decompress a 1MB chunk (or more if necessary)

So yes, it's a constant.