After lithium extraction, there's still a brine with roughly the same salt concentration, but likely with more other pollutants. You'd just be kicking the problem down the road.

But the issue is dumping the brine into the ocean as the only economical way to deal with it. If someone can make a significant profit off the brine, it may be feasible to truck it to a lithium facility then deal with disposal in a way that isn't just "dump it in the ocean and pretend it's not a problem".