Yeah, the FGO version of Asterios/the Minotaur isn't, y'know, actually a capital-M Monster. If anything, that would apply to his dad king Minos for throwing a child into a labyrinth and then getting it into his own crazy head that the only way to keep the hulk there was to sacrifice children to him. Asterios never demanded the sacrifices, he was perfectly happy to stay in the Labyrinth because that was what his dad told him to do and he desperately craved his father's approval as most children do. That was all on King Minos.
Theseus didn't realize this until after he'd already killed Asterios, and it completely soured him on the whole kingship thing. "Asterios should be king, not me."