It's rather the amount and perception of amount added. Usually in recipes while cooking, the amount is more controlled and distributed throughout the dish. Adding further salt adds more uncontrolled variability to the sodium intake in ones' diet
>The original commenters point still stands though right?
Yes!
> Also isn't addition of salt often a sign the chef/cook messed up and under-salted a dish?
Being a question of taste, literally, it is a subjective question.
IMO you should respect the choice of the chef/cook, and if we are only talking of the "messed up" dishes, then I hope the cook dont mess up that often that is justify to add a salt shaker on the table.
On the other side you have people that add salt to every dish, and this before tasting it, those one are on the dark side!