With underwater photography there is really not a one size fits all solution and you will need to adapt your equipment to the diving environments your frequent. Most of my dives are deeper technical dives and my rig is customized to those needs for the extremely harsh environment.
I am currently using a Panasonic GH5-S in Nauticam housing with an external SmallHD video monitor also in Nauticam housing. I am not shooting with strobes and instead utilize either Keldan video lights or UWLD video lights. All of this has been picked based on my needs for often shooting in extremely low to no light situations. I also frequently dive a closed circuit rebreather as it allows me to stay longer and is necessary for the deeper dives I often complete. However, I recommend a CCR for all photo and video shooters as it will increase your marine life interactions by eliminating the bubbles and noise associated with normal SCUBA diving equipment.
If you have any questions about what camera setup may be best for your underwater photography or video needs just shoot me a message on the contact us page and I would love to geek out over photography options based on the type of diving you do and your ultimate goals in creative imagery. In short I love to talk diving and photos so don't be shy.