Traditional Swiss rosti is just shredded potatoes fried in butter or suet. That's it. They don't contain any of the additional ingredients in that potato pancake recipe. But they are properly seasoned with salt and pepper. Rosti is supposed to taste of potato.
IMO people who complained that the potato pancake recipe is "bland" probably didn't use enough salt. There are more than enough herbs in that recipe, not to mention carrots, onions, and lemon juice, etc. to give it "flavor."
So I'd say salt.
Less is not more. More is more and more is fabulous.