Magpie made for a pretty good villain (and didn't seem any more overtly sexy to me than the girls on BTAS)
As I said, it's not about sexy vs. not-sexy, but about the execution of the sexiness. Poison Ivy aside, most of B:TAS's femmes fatales were dressed in garb that was skintight and somewhat fetishistic but not very skin-baring at all. Catwoman and Harley were fully covered except for their faces. Red Claw had one bared arm and shoulder. Talia wore a full jumpsuit with just a bit of decolletage. Calendar Girl wore skintight dresses and leggings and full-face masks, covering everything but her hair. Roxy Rocket wore a moderately low-cut top under a bomber jacket, but aside from that bit of cleavage, she was pretty well-covered and quite practically attired for her modus operandi. Discounting Francine Langstrom (whose clothes were torn by her transformation and magically mended when she changed back), the only villainess I can think of in B:TAS/TNBA who was really scantily clad was Emmylou Brown in "Critters," who wore a midriff-baring cutoff blouse and Daisy Dukes -- but at least that looked practical rather than something you'd see on a strip-club stage. Ivy's strapless one-piece bathing suit and leggings were the only B:TAS villainess outfit with wardrobe-malfunction potential, but since she was generally presented as a less physical opponent, and one whose primary MO was as a seductress, that made sense.
And at least Ivy's outfit had a certain elegance and subtlety to it, certainly a lot more than Magpie's.