The thread might be, but the conclusion isn't.
Yes, the oceans might have had a much greater salinity 3.5 billion yrs ago. But I think large multicellular organisms have evolved much more recently, perhaps in the last 3-4 hundred million years.
And if an organism evolved in a fresh water environment became exposed to salt, it would do one thing. It would die. The dehydrating effects of salt in the diet would throw it totally out of kilter, a sort of feedback, where it started to dehydrate, drank more salty fluid to rehydrate, saline suicide.
It is also interesting that there is greater diversity of life in salt water environments than in fresh water. A part of this was the evolution of calcium based bones. Marine animals without bones depended upon the free calcium in ocean water. With the evolution of bones, fish could move into fresh water and survive because their bones would act as a calcium reservoir.