During my last trip to Raja Ampat I had the chance to compare a Sony A6400 with the 10-18mm f/4 lens to the GoPro12 with AOI UWL-5 wide lens for videos. My original plan was to use the Sony camera mainly for macro and have the GoPro setup for wide angle. However, most of the dives were more appropriate for wide scene videography. So I used both camera very similarly, therefore, I produced many similar footage, which is a good opportunity for comparison. I tried to max out both systems. Sony was on XAVC S 4K, 25p 100M, while GoPro was used with GoPro Labs (4K 60p, highest bitrate). You can see the setup below:

I've uploaded two videos with many footage on my YT channel. The perspective is a bit different but they can be compared. There was a recent thread about the "cinematic" application of action cameras. I think the GoPro is not that bad but I observed many optical errors.

What do you think about the results?

You can buy currently the GoPro set-up around 600 euro, while the cheapest wide-angle option for Sony A6400 (with this zoom lens) is 1750 euro when a Saltedline housing (400 euro with 6" dome port) is used and not the more expensive Nauticam case (there would be not much optical optical improvement going for the more expensive housing).