I agree with what you are saying but I think I may have oversimplified just to stress a point.
Radicals build up to form different kanji, but once you get to kanji, they don’t build in to bigger kanji, they just pair up to form words. (With the exception of kanji that are later used as radicals, in which case, your point holds)
Kanji get used again and again, but if you find a word that you don’t know, then you soon find out which kanji you’ve forgotten how to read. You in turn end up studying ONLY the ones you have forgotten. The time spent waiting for new lessons due to 1 or 2 leeches, can instead be spent on new kanji that your mind absorbs easily.
I guess we are approaching the same thing from two different ways: either spend more time at the start, so you never have to study it again; or spend more time getting it wrong and having to redo the items. I think the latter is more efficient as most of the time, I don’t forget the meaning by the time I’ve guru’d a word that contains the same kanji.
Also, if I remember how to read the kanji based on another word, then I’ve got another mnemonic device to help me remember for future words. If I forget for example that 王 means king, but I remember 王子 means prince (and I also know how to pronounce it because it’s just a word I’ve always known), in the future when I come across 王妃 I can use my knowledge of 王子 to deduce the meaning. (even if I forgot 王 on its own.) The words thereby reinforce the kanji, so you don’t have to get hung up on the kanji. WK seems to be designed to review earlier kanji with new jukugo words that reuse them in the later levels.
In my experience, native Japanese speakers often don’t know the meaning of a kanji in isolation. They can however, read any word that comes their way and know what it means. Same with radicals. Native Japanese will often have a special name for a radical (when trying to describe how to write their kirakira names with Nanoji or ateji) and an innate sense of the radical or kanji’s meaning, but they don’t know a specific or meaningful name for it like one that has been ‘given’ a name in WK.
It’s like suffixes and prefixes in English. Most of us don’t know Latin but if a word starts with ‘pre’ or ends in ‘ology’, we have a good idea of what it means. I knew what biology meant before I knew what ‘ology’ meant. When I came across scientology for the first time in…maybe junior high?, I associated the ‘ologies’ and subconsciously associated it with ‘the study of~’. Doesn’t matter if I know ‘ology’ or ‘王’.
I guess I shouldn’t have used Math as an analogy. It doesn’t work because you can’t do calculus without algebra, which you can’t do without arithmetic. That’s not how WK works for me. I was trying to compare one unrelated kanji (let’s call it ‘math’) with another unrelated kanji (‘science’). I wasn’t trying to emphasize the progression of math skills. Anyways, I think we have different learning styles and that is swell. 
Edit: just looked it up and apparently I still don’t know the meaning of ‘ology’!
