If I remember correctly (ha), WaniKani is actually ordered by the simplicity of the kanji, as they also point out that children can only start with simple concepts but non-native adults have the concepts covered but will struggle with complex kanji.

You do. Most off the early levels are kanji that a first grader would know, and it very loosely stays organized by grade level, with a lot of allowances.

The true masochists go for Kanken level 1 (which has almost 90% fail rate even for native test takers, and those are already the self selected sample of people mad enough to try the test).