First of all, the writing structures of the two poems are different. "Farewell to Deputy Du DuDu to Shu" is to write about scenery first, then comfort, while "Bai Xia Tang Shaofu" is to establish friendship first, then write about scenery, then comfort.
Secondly, the two poems have different purposes. Specifically, "Farewell to Vice Governor Du to Shu" is mainly to comfort and encourage friends. Despite the sadness of parting, it conveys an optimistic and open-minded attitude towards life. Yi Zhu Tang Shaofu in White House shows more sadness of parting and reluctance to part with friends.
Generally speaking, the two poems are different in emphasis and expression when expressing sadness.