I used a GoPro Hero 3+ and a pair of 1500 lumen lights for around two years when I was first learning to dive and shoot underwater video. It was a great little camera for landscapes as well as fish and people portraits. As I became more interested in macro subjects, I purchased a Macromate Mini but I found it to be very difficult to use due to the fixed focal length and narrow depth of field.
I badly wanted to upgrade but I could not afford a DSLR or mirrorless setup at the time. So, I e-bayed a camcorder rig using a Sony CX580 in an Ikelite housing. Although I was still shooting 1080p, I found the image quality to be much improved and the larger rig with in-camera stabilization provided much smoother footage. The ability to zoom also allowed me to go semi-macro on larger subjects.
After a year, I stepped up to a Panasonic LX100 in an Ikelite housing. This was a huge improvement in image quality with the ability to shoot 4K video on a mirrorless sensor. Over time, I added various wet lenses and a pair of 8000 lumen video lights. I have also added numerous floats to dial in the buoyancy of the rig and a homemade quadropod. I am on my second year with this rig and I have still not outgrown it.
As my abilities continue to improve, I will eventually move up to an interchangeable lens MFT system. In order to manage cost, I may look to buy a used GH5 setup when an obvious successor is announced and housed. I am very keen to shoot 4K60fps output to 24fps with Cinelike profiles and much higher bitrates than the LX100 offers. Here's hoping for a GH6 announcement in 2019!
N.B. I still carry a GoPro Hero 7 Black for above water shots, like goofing around on the dive boat, when the LX100 is housed. I also have several other models (4 Black, 5 Session, etc.) that I use for other activities such as mountain biking and downhill skiing. I am a huge fan of these little guys!