Why is WaniKani worth using beyond lvl 15-20?

I mean, WaniKani teaches most of the Standardized kanji (There are 2136 Standard Kanji Jōyō kanji - Wikipedia) so I don’t know how that could get anymore “core”. I have seen others who have made it to level 60 say that there are many uncommon words near the last few levels, but that isn’t to say they don’t ever come up at all.

WaniKani actually teaches 2055 Kanji and 6360 Vocabulary, which is a non-negligible amount greater than what you claimed (maybe your sources are outdated?)

AFAIK WaniKani doesn’t claim to be a JLPT study service, nor does it claim to prepare anyone for the JLPT.

I agree that sentence mining should be done in tandem with WaniKani to broaden vocabulary around your own interests, but I disagree that WaniKani isn’t worth it past lvl15-20 since there is still a lot to be gained from the other 2/3 of the levels.

I’ve found a few userscripts that may interest you: