First, the object of address is different.

"Xiong Xue" was originally a title among students (contrast: in the old society, the imperial examination was called "Brother Nian", regardless of actual age).

When the teacher addressed the students as "Xiong Xue", he felt very humble (in the past, Mr. Rong Geng wrote to the students, all of whom were called "Xiong Xue", which was famous. )

"Senior" is generally used to address seniors (especially those who are obviously taller than themselves but are not very teachers).

Unless you are really much taller than you, it seems unnecessary to call your contemporaries "seniors" (but that seems to be flattering).

Of course, there is also a habit problem. Maybe in a certain circle, everyone is used to it, so there is nothing to say.

Second, the ownership relationship is different.

"Senior" has no gender restriction and can generally refer to boys and girls; "Xiong Xue" can only refer to men.

Third, the sources are different.

Xiong Xue has no source, and people use words generated by habit in their daily life.

Senior: Cai Yuanpei's My Experience in Peking University: "In that year, the government appointed Yan Youling as the president of Peking University ... changed to He Xihou and resigned soon. His agent is Hu Cishan, a senior majoring in engineering.