> Try have them be educated in a kana only system and then have them try read it.
I can't, because there are no native speakers who learned that way, as I'm sure you know :D
But there are many learners like that, and my experience in Japan is that anyone who doesn't learn kanji has a very low ceiling on their vocabulary, even if they use the language daily for decades.
Because the reality is that it's hard to memorize 1K kanji, but if you do it then it's relatively easy to learn 10K+ compound words. Without kanji, to reach fluency somebody would have to memorize 5-10 completely unrelated meanings for "kouka", then 5 more for kakou, and so on for every combination of common single-kanji readings.
I mean - if you're in Japan, you surely know people who try to get by without kanji. Do you know any who've reached fluency? Like who could use and understand 5-6 different "kouka"s without any idea of the kanji they use? If your premise here is true then people like that should be the norm, since learning would be so much easier for them compared to those wasting their time on kanji?