While I wish we'd get more new servants, as an assassin she is pretty powerful, at least from what I can tell.
She's still not as good as Assassin of black/Jack from what I see. Jack hits hard, fast and multiple time that it's ridiculous.
Although Heroine X's skills are pretty interesting, a timed stun which was annoying as shit when you fought against her, and her NP was on par with Herc's.