ok, first things first, to kick this off: there’s no scientific proof that interleaving or other methods work better or worse for vocab acquisition.
there is, however, scientific evidence that points in the direction that learning vocabulary by topic (bird names) or other grouping (antonyms, synonyms, same this or that) is less effective. this includes learning a set of vocab items in specific order (word lists, for example iverson method).
wanikani doesn’t teach such lists.
yes, radicals, kanji and vocab are connected, and usually, if you get one right, the others are correct as a consequence, but if you think about it, all the words you learn and the radical are part of the neural network that makes up the memory of that specific kanji. 日にち、日々、日付、日曜日、日焼け and so on are all single strands of the kanji you just guessed right, and it’s perfectly cool, because that’s what you’re here for.
since there are no thematic (et cetera) lists of radicals, kanji, vocabulary here, there’s no need to introduce another layer of interleaving by making reviews harder artificially.
i’d argue that when you work on your reviews and you focus enough over a long enough period of time, you go into the flow, which impacts your learning process positively. by testing reading and meaning together, you activate both bits of information in a timely manner and reinforce them at (almost) the same time.
(you go into alpha state when you’re engrossed in a book btw)
that’s why i think Tofugu misunderstood something there … which is no big deal, because mods exist, and everyone’s free to do it their way, just as @Omun said.
and tbh, i don’t think it’s even a big deal in the grand scheme of things
2-3 years of wanikani are nothing compared with how long some of us have been studying already.