WaniKani is not primarily a vocab learning app. It uses vocab primarily to reinforce and expand upon the kanji readings and meanings, and to help embed the kanji into context to aid remembering them.
I have tried KameSame in the past, and for what it is, it is a good app. However, it was too unstructured for me, and I ended up adding way too many random words and it became overwhelming to review everything in my review pile.
Recently BunPro has added vocab support as one of its current Beta features (to access, need to opt-in to the Beta features in your Settings), and I’ve discovered that I really like it.
It is still in Beta, so it’s not 100% smoothed-out, but it is still easily usable and – more importantly for me – is at least a little bit structured.
For now, it has 1100 vocab entries in the JLPT N5 category, and another 1100 in N4. These are just in a basic dictionary-like order, which isn’t the greatest. But! When you access the Beta features, you also get access to the new Decks feature, which presents existing grammar & vocabs in different orders, according to different textbooks and other learning resources.
So, for example, if you use the Marugoto decks and the Genki decks, you’ll get the vocab according to how they are presented in an introductory textbook. This is very useful for getting a good solid base of vocab words to start yourself off with.
Once I finished off all the vocab (and grammar) from all the introductory textbooks, I switched over to the built-in BunPro deck for JLPT N5 to finish off the N5-level vocab (it’s not 100% of N5 vocab, just the most common 1100 (for now!), but still plenty).
After that, the other textbook decks only have grammar (no vocab (yet!)), so I switched to the BunPro JLPT N4 vocab deck, and I’m working away at that.(about 68% through so far).
The BunPro vocab reviews are recognition-only, so you only have to give the English equivalent of the word/phrase, which means that reviewing them is not as mentally taxing as say WaniKani vocab where you also have to produce the correct readings. [BunPro does provide furigana, though, so you can also learn the readings; you just don’t have to produce them.]
This means that you can go a lot faster than with WK vocab, learning many more words than you would be able to in WK. Thus, I find this a much better alternative than WK for the purposes of reading vocabulary, which WK isn’t really/primarily meant for anyway. So, it’s a good alternative/supplementary tool for learning vocab. And it’s more structured than KameSame, IMHO.