I don’t think I’ve ever found a "pass a test to skip content ‘you already’ know system that was ever actually competent. Why? Such tests would simply be summaries of the content, meaning you’ll have significant gaps in your knowledge. I successfully tested out of more than 10 classes in college, and my friends had homework with stuff I’ve never seen in my life from those classes.
WaniKani is designed with a particular system in mind, specifically utilizing its custom radicals and mnemonics to create its SRS system’s scaffolding. Even if you used a 90% kanji test system, you would be sacrificing the vocabulary, meaning you’ll get in trouble later on with alternate readings you SHOULD have learned early on. あ is the reading you learn for 合, but by level 25, you see ごう most commonly.
As for the comments about natives saying such and such word is useless, that’s just silliness. I’m sure most native English speakers would tell you knowing the original meaning of gay is useless due to its almost exclusive use for homosexuality, but if you don’t learn that meaning, you’ll think that everyone dresses up like homosexuals if you listen to Deck the Halls (don we now our gay apparel).
Honestly, if you have any need for a kanji learning site, you don’t know enough Japanese to claim what is actually useful or not useful. I’ve been told 語る is never used, and I honestly don’t think I’ve heard it used alone, but unless you want to go around pronouncing 物語 as ぶつご or ものご, be my guest.
As a side note to the “worthlessness” of certain words, I had a middle school student write bread as 麺麭 on the blackboard. In another class, I found out that 小麦 can also be used as 当て字 for パン.