While I definitely agree about video decoding, encoding still is a valuable measure.

With inter-frame delivery codecs the hw encoder always focuses on speed, with a lean towards file size as well. It makes sense for most consumer use cases. 15x faster perhaps sure, but you might end up with a file almost 10x larger while still lower quality than a decent CPU encoding. Also the more off the beaten path of rec709 and rec2020 you go the less certain you can be that the hw encoder supports things.