It was a stupid idea 110 years ago and still is. You have no idea if the ocean is in equilibrium today, has been in the past or not, so salinity could have been going up or down or staying the same at various times.
Actually, we do know this. It can be determined from the various geological salt deposits around the world left when water from Oceans has, for one reason or another, been cut off and then evaporated out. And the result from these tells us that the salinity (and proportion of other disolved ions) has varied over geological time but not by vast amounts.