The “brine” at the outlet pipe is just 2-3% saltier than the ocean water at the intake pipe. The impact is not zero, but it is very low if done right.
Sea-water is about 3.5% salt by weight. Are you saying that the brine water coming out is 3.5 * 1.025% salt, or that it's 5.5% salt? Do you have anything you can cite? What % of the water that goes in the inlet makes it to the "brine" outlet?