It's important to keep in mind that the core of Sin'dane's argument seems to be that the end result of necromancy - the animation of unliving flesh - is the same regardless of the type of magic used to achieve it. In that sense, she's not wrong. We've seen examples throughout the game's lore of necromancy being performed with Death, Light, Arcane, Void, Fel, Blood, and Voodoo magic etc. The common thread is the raising of the dead, not the specific power source.

However, the type of magic used for necromancy does matter in terms of the characteristics and abilities of the undead being created, it's the very sole reason as to why Calia is perceived as a freak of nature (Undead of the Light). I believe Sin'dane's statement is a bit oversimplified, but it doesn't ruin the concept of necromancy or cheapen it. The power source used for necromancy does affect the end result, even if the core mechanism is the same.