Just out of curiosity, WHY is it doing so well? It's not the 1st appearance of the current Killer Frost at all. It's not her origin, it's not her backstory. It's nothing except a first appearance of a character that's not in any upcoming movies, television shows or even animation.
It's like saying "Green Lantern is hot". Then I'd have to ask "which one?"
Most likely for the same reason that MSH 18 went through the roof, even though none of the characters are the same as the movie Guardians (Yondu did appear, but that character had little in common with the original Yondu). People will go back to the "first first" and that book will spike, regardless of the retcons and changes that have been made to the character over time. At least, that is how it is playing out right now.
I sort of get the confusion with the Guardians of the Galaxy simply because it's a 'group' and there's no direct comparison to some older versions of the Guardians. In that regard, it's not an entirely bad idea to grab the 1st "1st".
But it should be markedly simpler to establish the lineage, origin or appearance of a singular character. For instance the 1st appearance of Star Lord. If folks wanted to find that, it'd be fairly easy. To find the current lineup of the Guardians as found on-screen, you'd have to get more recent of course.
Showcase 22 will always be a grail, but if there's a 'new onscreen GL' that isn't Hal....I wouldn't expect it to spike unusually. I'd expect the 1st appearance of whatever incarnation of that 'new onscreen GL' to pop a bit.
Same deal with this issue: there's like a bazillion Killer Frosts. The one slated for the small screen has no relationship whatsoever to the prior Frosts. Even in the multiple animated series and animated movies: more than 1 Killer Frost has been portrayed. DC is obviously retconing or reconing this character because 'she' is utterly confusing and it'd be much simpler to have the new one be the definitive one. Up until the Forever Evil storyline she didn't even have a proper origin story.
That is all logical and well-thought out. I'm not sure the market responds to either of those concepts.