Amongst various views of the background, it is said that Yoshiharu assassinated Katatoyoin order to recover the authority as the family head, after struggles between Katatoyo's authority and Yosiharu, the young family head, since Katatoyo was such a well respected chief vassal as a meritorious retainer of Rokkaku clan since the period of Sadayori and well admired of as "twin To (phonetic alphabet of 藤 後藤, GOTO and 進藤, SINDO) of Rokkaku clan" that he held the authority to execute administrative affairs on behalf of the family head.
理由は諸説あるが、賢豊は定頼時代からの六角家中における功臣として人望も厚く、進藤貞治と共に「六角氏の両藤」と称されるほどの宿老で、奉行人として六角氏の当主代理として政務を執行できる権限を有していたことから、賢豊の権力と若年の当主・義治とが争った末に、当主としての執行権を取り戻すために暗殺したと言われている。