It depends on the situation. more powerful light gives you more options of what video you want to shoot. These lights still need variable output though. Now thats difficult to make consistent. Say in still water and it is gin clear I would use as much lumen as possible with wider beam. Some UW wrecks are difficult to lit properly for a wide scene. In some waters I would use a narrow beam. With flood lights a condenser lens will work and produces a nice long throw beam. Even with these less powerful light you could do a lot with cameras with high ISO and DR. Well a year ago lights with 2000 lumen is nothing to sneeze at. I say that because now there are portable LED lights that could pump out more than 22000 lumen. But cost over 2K. It is only a matter of time when 4000 to 6000 lumen become the norm and price will drop. It all boils down to demand. Not many would spend a princely sum on a light. More power means more heat generated, bigger power demand, heftier electronic ballast especially for dimming. Color too. High CRI (color Rendering Index) and high power is quite complicated to do. Again difficult for dimming and maintain same quality of light without any flicker. I have seen some high power ones but these are not yet up to par with Keldan or the like. I am sure the Chinese companies is more than capable. R&D and prototyping is costly. Powerful battery is also the limiting factor. Battery tech. with enough juice and light weight for powerful lights is really limited to Li-ion and Li-po. Li-Ion I see at present is the only option as it is in pressurized containers. Li-Po is out of the question for powerful UW lights. Too dangerous.
One way to get more light is to get a few of these and bundle them together. I tried four lights in two, two configuration. Output per light is 2500 lumen. Total 10000. Total cost is still less than the cost of a single 6K or 8K light made by premium brands. Not as convenient but does the job like you say