In modern content designed for people over the age of 10, spaces are uncommon as kanji does a lot of the word division duty. It’s also a little unstandardised: is 遅くなって初めて (when I first became late) one modified word or three words? Since regular Japanese writing doesn’t care as much about word partition, there is no standard so you could so anything from おそくなってはじめて to おそく なって はじめて when spaced.
I reckon a lot of these full kana games would be harder even for natives if they used a more standard space free style.
The people at Kanamoji Kai (all native speakers) are well aware of this too, and their website even has a section on 分かち書き (word separation). They use the example スモモ モ モモ、モモ モ モモ、モモ ニ モ イロイロ アル。 to illustrate that using spaces is a must if we switch to kana-based writing.
>> these full kana games would be harder even for natives if they used a more standard space-free style
This is true, but I take issue with your use of the word “more standard,” as USING SPACES IS THE STANDARD in full kana games.
Any form of writing reform, by definition, involves moving from the current standard to something that is initially non-standard, right? Korea got rid of kanji and now uses spaces with Hangul. In my opinion, it’s way easier to adapt than most people think.
(For the reader, Japanese has a lot of homonyms since it has a comparatively limited set of phonemes. Specifically a problem in writing due to lack of context, spaces and lack of tonality that can help disambiguate the language when spoken)
The obvious way people handle it in speech is by picking words that are clearer in context when homonyms might cause confusion. If you consume any Japanese video content on YouTube etc, it’s very common for speakers to say a homonym, instantly notice the ambiguity, and restate it using a clearer word or brief explanation, which they could, at least in theory, do in no- or low-kanji writing too.
同音異義語の区別に不可欠な漢字の廃止は不可能か？(Is abolishing kanji -- which is essential for distinguishing homonyms -- impossible?)
https://www.kanamozi.org/hikari932-0704.html