I think it's smart balancing the need to get cargo with it also dragging you down - especially paired with depleting oxygen. I think 2 things could help:
- When you're fully loaded with cargo have the player still be able to go up, but very, very slowly. It seemed like I was doomed if I filled it to 80%
-It took me a while to find the boat to be able to unload the cargo because it was hidden behind the HUD element for life/oxygen/cargo. Maybe moving that to the middle would help.
I had fun though - got a 7.6/10.