The dead sea is 10x normal ocean water salinity. If you remove most of the water from Pacific ocean water and pump the brine back in to the ocean, you are basically pumping water from the dead sea in to the Pacific creating a huge dead zone until it dilutes back to normal concentrations.
It isn't the overall salinity that is impacted but local conditions.
Even though the comparison is hard to take seriously, there is probably nothing we can do at our current societal scale to make the Pacific Ocean into the Dead Sea equivalent. Ocean acidification from all the GHG pollution, now that seems to be possible. DeSal scale is just not there and we don’t actually need THAT much extra water for cities. Agriculture could be another matter, but economics are not there yet.
It isn't the overall salinity that is impacted but local conditions.