Dear Yankelle,
The term “Sar HaTorah” is not new. In the most recent era, it was given to the great marbeetzai torah. The Netziv. R’ Chaim Brisker, R’ Aaron, R’ Moshe, R’ Shach, R’ Shmuel Rozovsky, and R’ Chaim Shmuelevitz. (I know there other factions that use the title. But that does not relate to my point.) It Switched with Rav Shmuel Birnbaum. He was not a public figure and he had a small shiur in the Mir. The last ten years of his life, his shiur grew (Until he was ill.) and he gave shiurim all over. [Also, a high percentage of his talmidim became influential marbbetzai torah. With R’ Chaim Kanievsky it switched to a public figure who personifies the Torah.