I just had this chat with a friend who was pondering a Nikon Mirrorless vs a DSLR, so I'm tell you what I told him. The weight of a specific camera body and lens won't be substantially different than any other comparable body and lens. They aren't the problem. It's all the other junk you need to take a few pics in the water. Will you be carrying strobes and batteries, multiple lenses, arms, domes, rings etc? And then there's the housing... They all add up.
What I can tell you is that my D500, Aquatica housing, two Ikelite 161s, a Tokina 10-17, Nikkor 105, Nikkor 60, a wet, diopter, mini-dome, cords and a few tools, all jammed into a Pelican 1510 roller case is about 43 pounds. I also tote an 8" dome and macro port in my clothes bag. and then in a backpack, a second D500 body with a Nikkor 12-24 and maybe a crappy topside zoom. Oh, and a 15" MacBook.
So basically, my camera gear is about the same weight as my dive gear. I take a few clothes, but mostly to pad other gear.
In my next life, I'm taking up badminton,