Cannot offer any data on that but I experimented with a SD TV series episode. HEVC and AV1 ended up at the same file size (few kilobytes difference) but encoding AV1 took over 10 times as long using rav1e.
Considering lossy encoding, you cant compare file sizes without comparing also quality, or you're just comparing default settings. I can make a tiny mpeg1 file (which will just be a pixel soup)