I mean that it's a load of bullshit from an out of story perspective. Not that Bolvar is a liar, but that Bolvar is a hypocrite guilty of much worse and that the writers are hacks for casting the Lich King, the poster boy for undeath and upon who's val'kyr Sylvanas's whole necromancy is predicated, as a legitimate death entity materially different than she is. The Lich King is a creation of the Burning Legion created for the specific purpose of disrupting 'balance', which is itself a meme, to set things up for their invasion. He's not some cosmic constant. He's not even from Azeroth, he's 33% alien.
Hell, while Sylvanas raised a lot of people in Cataclysm, her doings in BFA, which include several dark rangers and like four people, of which two have died and another has gone rogue, pale before Bolvar, who's standard recruitment was robbing bodies to enlist into the Ebon Blade world-wide in Legion and attacked the Silver Hand while raising their dead as ghouls to attempt to rob Tirion's grave. This being an ally of his during a war with Satan, whereas Sylvanas has raised people hostile to her while at war with them. Bolvar has zero legs to stand on.
So does Ol' "A small loan of a million (unwilling) souls" Bwonsamdi, but beside the point. The whole idea of a balance of souls is bunk, because the cosmic forces are inherently in competition for souls and the individual death entities grow more powerful the more souls they have which by default encourages imbalance.
@
Maljinwo
It was someone in the devs suddenly realizing they had no idea why Sylvanas was made Warchief and being told to make something about g ghosts or some shit while they think it up.