This is legacy stuff. Gaining a few bonus sorcery points for sacrificing hit dice is thematically appropriate, as well as the Ghul Lord's magic disrupting normal magic. While the first feature could belong to any death-themed sorcerer, here we are firmly in the domain of the ghul lord.
More legacy material. The idea is the ghoul lord can manipulate raw necrotic energy to cast spells. This lets them get a blasting spell they need easily, and a few utilities though they may be costly. Again, this makes this ghul lord specific, rather than just death sorcerer.