She's okay here:
It's probably better to show instead of tell I guess.
All four of the Avacyn angels have DD tits and thighhighs. They all show off their wonderful model figures in
that pose where women arch themselves back and pull up their legs ever so slightly to show off all the goods.
But you know, those are actually minor details. Each of the angels has something going on that draws your attention first, and then, once you look closer, you notice they're all smang-worthy. Avacyn and Bruna has their spears, Sigarda and Gisela have wicked halos. They're angels before they're hot women (okay maybe not Bruna).
This is not true of Liliana, and hasn't been true of her since her very first incarnation, as Charlequin pointed out. The less said about Argyle the better, so let's look at Dark Realms, and then Ortiz' Lili. The first thing you notice about her is that she's not wearing much. Oh, she has some kamehameha thing going on in her hands but that seems like an afterthought. Her head is very small, frighteningly so. As is her waist. Frankly, there's not much to the art aside from her body... and the strange leather-y clothing. This isn't really a matter of "female character who's comfortable in her sexuality" but "cameraman making sure to capture her tits and abdomen".
You can make an argument that they're using the art to showcase this "sexual" side of her (a side that doesn't really come up in the fiction, for some reason?), but I highly doubt most Magic players are up to date on their lore and DailyMTG short stories. They look at Lili and they'll see a hot girl. Wizards knows this, and tells their artists to appeal to this market specifically. There can be all sorts of reasons for why Lili never seems to wear very much, but they all seem to be circumstantial.
While we're on the topic, I'd like to point to Endless Obedience (above) and Liliana's Caress.
These are both cards with effects and names that would work well with her purported "strong female character who's unafraid to flaunt her sexuality" theme, but this element is notably absent from both these cards. Thus, I can't take seriously the idea that Wizards wants Liliana to be a person who celebrates her sexuality. Or if it is, it's minor enough to not be worth enforcing for non-premier cards, aka, planeswalkers.
Onto Ortiz' new Lili.
Clearly, she's following the style guide, because Lili's wearing the same outfit she wore at the end of Innistrad. I don't care to speculate on Ortiz's intentions because that's just rude, so I'll just talk about the piece itself. First, the camera is zoomed out, like for the AVR angels, and yet, it's impossible not to notice her bare skin. The contrast between her skin and her clothing demands it. The background is a gray, nondescript setting of fire and destruction, all of which makes her body pop out more. For stage props, we have these truly thirsty zombies that likely represent the game's male, tweenage audience as they ogle and hoverhand Lili. Come to think of it, this art would be really good for Endless Obedience, much better than the original was, which brings me to my next point.
Whatever Ortiz' own tastes, it's pretty obvious that the commission specifically asked for these zombies, Female necromancers as "mother/dominatrix" is a pretty common trope in fantasy, and this is what they were trying to evoke here. I think this one leans firmly toward the dominatrix side. Why? Replace Liliana with a real model, and the zombies with real dudes (note how none of them look even vaguely female). What do you see? A beer ad. She could be holding a can of Bud Light during the Superbowl.
This, I imagine, is the thing that really rustles people's jimmies: the way Liliana is just consistently conceived of as a model instead of a black mage. Or rather, that "black female mage" seems to be synonymous with model in Wizards' visual design dictionary. There's nothing wrong with this in a vacuum, but when you look at how often they're equating the "corruption" aspect of black with "sexuality", and applying that connection almost exclusively to females (Tasigur being a notable recent exception), well, that paints a different picture doesn't it? We all know where the idea of "corruption = sex" came from, and its origins aren't women friendly at all.
For the record, I like Ortiz' painting a lot. It's gorgeous, evocative and I can tell she went out of her way not to draw Liliana with a wasp thin waist and a xylophone rib cage. Ortiz's Lili probably eats full, hearty meals in between subjugating backwards peasant villages. But the powers that be demand Lili be a sex symbol and a sex symbol is ultimately what she drew.
Yeah Thoughtseize is pretty damn good though 
