It’s this guy:
Doesn’t include Absolute Beginner Club picks, but still helpful, hopefully.
I’ll add my vote to the slow down camp. It feels really horrifying when you’re gunning along at the beginning to consider the prospect that it might take you a few years to finish WK 
but actually, after a year’s break and taking it a bit slower now, I feel fine about taking ~3 years to reach level 60.
Reading along with the book clubs here has consolidated my kanji knowledge in a way that wouldn’t have happened if I’d focused solely on WaniKani, and going through levels 40+ I know a pretty good chunk of the kanji / words in each level already thanks to reading, so the whole experience is just much more pleasant. I get to use my knowledge, I’m doing a fun activity and feeling like I know some Japanese, and WaniKani is a bit easier! What’s not to love?
OP, I think you’re underestimating how easy it is to judge the difficulty of a particular book, especially by WaniKani level and JLPT level. One book is not going to neatly align itself with N3 grammar without ever using N2 or N1 grammar, nor do most readers have an encyclopedic knowledge of which levels these grammar points correspond to. The exact same principle applies to WaniKani level (and, if the book has furigana, WaniKani level really is a little irrelevant, except in terms of perhaps indicating you’ll need to look up less vocabulary).
The best we can do is give our general impressions of difficulty, but what makes a book difficult for me might not be the same for you.
I would point out that, you know, the Doggy Detectives book club starts on the 6th… 