Yeah, dips are normal. But seeing no copies of later issues is a louder statement than anything. I find anywhere from 0-3 copies of later issues from some series, which is nice to know but also frustrating if I'm trying to get it.
I absolutely agree that current writers should really look at their run as possibly ending at any time. So tell as good a story as you can, and don't commit to long-form arcs. Unless you're King - then you can just do whatever you want apparently. Here's the kicker though, comics should be and mostly is a meritocracy. Valkyrie could be really well written (doubt it) but if no one gives a fuck about another Jane Foster shoehorn then it's not going to sell... It's a gamble, that's the business. But don't rest on your laurels just because you know you'll be fired into your next "mini series" or "team-up" book, GAIL.
It's fine, the artwork itself is decent enough, but you know what would make it better? Some shit going on around her. I'm not going to hang up that shit on my wall, but what I WILL hang up is Catwoman Vol. 3 issue 76, Adam Hughes is a fucking BOSS with covers, and they are easily my favorite to hang up on my wall. Another good indicator of good work? I have that Catwoman issue memorized because it stuck with me.