Your experience is valid today but for a different reason: if you're comparing millions of tiny files there's a lot of back and forth. If you're streaming a single archive, it only checks if that single file has been modified.

Like everyone here I've no benchmarks but have got burned trying to rsync around too many small files.

I got into the « lot of small files » case, and I ended up generating a file list, split it and feed multiple rsync instances with xargs.