Saying it over and over and over again, to a point that drowns out the character's other features, and actual, you know, personality, is a way of reinforcing the way in which women are judged to an absurd degree on their looks.
As for Faye staring at Sven's ass, 1) no I don't remember that strip (maybe because it wasn't 5 of the last 10 strips where it happened), and 2) which actions count as sexist/inappropriate depend on the power structures in place. Women ogling men is not at all like men ogling women, because, in general, men do not inhabit a world in which they are viewed as objects rather than persons, and are rarely told that their worth is based directly on their appearance. And I don't mean "told" in the sense that people sit women down and say "now, listen, you are only as valuable as you are pretty". I mean the subtle ways in which society and culture and media (including, yes, allegedly "indie" comics that don't _try_ to be part of that system) present a particular picture of what the appropriate gender roles are.
Let me put it this way: women are expected to wear makeup, men are not. But it's not like men have magically smoother skin or more blushed cheeks. It's just that society doesn't put pressure on men to prioritize "looking pretty", because, in society, men are not devalued into mere objects of sexual conquest/interest.*
There is something empowering (in terms of challenging patriarchal ideals) about having female characters that speak frankly about sex, and do not consider their own bodies to be off-limits for discussion. But, in the comic, Marten, Faye, Dora, Tai, tall-dorky-guy and Penelope are all participating in the process of objectifying women through their constant discussion of Marigold's chest, and, as an author, Jeph is not employing this as a means of drawing attention to, or otherwise combatting harmful tendencies in culture (nor even as a way of commenting on them), but is also promoting the harmful social norms.
*I'm definitely not saying that social and gender norms benefit men in all ways. There are a lot of significant constraints on whether men can be open emotionally, and there is a lot of pressure to consider men more valuable if they are more aggressive and sexually virile/active. However, a) this also compounds the problems facing women, b) it is pretty clear which gender faces greater disadvantage from current gender norms, and c) the system is enforced and perpetuated, primarily, by men, who hold most or all of the major positions of power in government, industry, and media.