The very non-sexist nature of the series in general makes this stand out more to me.

Sure, you can say that not handling the issue in depth is what is causing me to think this is sexist. But isn't the lack of depth itself a manifestation of some bias?

I'm not trying to argue here that Erikson is some big time sexist, but the point is that he chose to show a culture that practices gang rape and mutilation of women, and then showed that the women support it and hunger for such a fate to befall their rivals. It is not so much the act itself but the repeated statements (and the actions of the women themselves... after all, it is the women that drag Hetan out) that really enrage me.

We're dealing with an abhorrent custom here. The least you can do is handle it well enough that it doesn't come off as sexist.

And while we do see the Bhargast trough Hetan and Cafal's eyes in MoI, the Malazans also move among them, and we in fact have one of them fight to become chief of one of the tribes! All we're told is that he can have is pick of women that night since they'd all be falling over themselves to sleep with him (IIRC). No mention of hobbling at all, not even as a discontinuous custom that would have been practiced on such an occasion.