Yes, exactly. ledsen is a feeling experienced by someone. Filmen var sorglig, jag blev ledsen 'The movie was sad, I got sad'. – It works the other way around too, if you say a person is sorglig, that will not be ambiguous as with sad, it will only mean that they are sad as in pitiable, not as in feeling sad.

No. Tråkig means boring, and would sort of trivialize the meaning.