This is just a quick audio test to compare the mics of the Hero 4 and 5 session. I think it does sound better, generally the 5 has a fuller sound and a little bit more detail.
Obviously these action cams aren't really designed for this kind of use, but I was interested to hear the difference. Considering the 5 is waterproof (without extra casing muffling the sound), it's a huge improvement for water sports and the like.
GoPro 5 Session vs GoPro 4 audio test