HarryMann, auv-ee is exactly what his moniker implies. He is involved in the AUV industry as an EE. We've conversed a bit. He's anything but dumb or ignorant of the underseas environment.
Something of note on my personal experience is that I've watched activities at levels a little below the surface and thanks to BP's many streaming videos under very deep water. I could see no salient differences in the way materials moved or the vehicles moved. Water does not get thicker or denser as you go down except by very small amounts. It's viscosity/pressure profile shows very little change until you hit the phase change that turns it into some form of ice. Water is NOT thick air. So you cannot infer much of anything from your experience with air.