Learning 2500 kanji from the beginning is a major cognitive task that shouldn't be a primary focus, nor is it in native Japanese language pedagogy. But learning the kana is simple, again I learned them as an adult and had them down cold in a few weeks of active classwork. My kanji retention is terrible, but learning materials almost always give the reading of kanji using furigana, and there are useful tools for annotating web pages, etc. with furi readings.
My grasp of Japanese is virtually non-existent, but I noticed this as well. Taking an example from the post, I find something like しっけ easier to parse than the romaji shikke. The latter form just feels clumsy for reasons I can't really articulate.
It also makes the pronunciation a little easier at times. If I read "desu", I read it with a fairly pronounced "u" sound. Reading です, on the other hand, I know without really thinking about it that the う sound is typically very short.
Really though, you can learn hiragana in a single sitting using mnemonic trickery and you can commit it to memory using a spaced repetition or flashcard system in a few days. Not learning hiragana and katakana seems much more of a hindrance than "wasting time" by learning it.
My book is geared specifically towards people who are to enthusiastically committed to learning Japanese, and want more information about the language they're paying money for to learn, with some assumptions about what that means: they, like me, and like many of my fellow students at the time, but not like everyone, want to learn Japanese properly, without hand holding because some grammar or some orthography is deemed too hard. We'll see whether that's the case as we learn, not as an assumption baked into the course.
Of course that method doesn't work for everyone, but for me, and for many others, but again not for everyone, getting kanji early was exciting, motivating, and awesome. I would have been angry at a promise of a better approach without kanji for half a year as a paying student.
So that's the book you get here, too: I am not making assumptions on how slowly you want material, this is a grammar for supplementing your course work, or deep diving if that's what you want to do. And if the Japanese used in the book is too much, too soon: it's a free book, find one you feel fits you better. But we're better off with a spectrum of works: rather than every book following the best methodology, we need all those methodologies, and then people who go hard, fast, can pick the hard, fast books, and people who don't can pick the slower, "better success rate" approaches and do well with those instead.
And another comment, https://news.ycombinator.com/item?id=12286516, expands on that a bit more.
Thank you so much for your hard work!
Also I think some example sentences in the book would sound awkward to native speakers. (e.g. "今日自転車で帰り中で転んでしまいました", "もっと安いのありましょうか", "お箸の使い方に慣れてない人に難しいです" (this may be a typo), "きれいじゃないで、明るい部屋です", etc.)
I think this girl gives better advice on how to learn Japanese:
As for odd sounding sentences: nice! let me know about them on the github repo. Link's in the side nav as the github icon, but the direct link is https://github.com/Pomax/nrGrammar/issues
I wrote this book based on that need. So step 1: learn hiragana, because after the introductory chapter you're not getting romanised Japanese anymore. However, because it's not a writing course, all kanji have furigana so that you can read every sentence. This book is not going to calmly and gently lead you through the Japanese grammar, it's meant as a proper "you need this book for a year at most, after that you should already know everything that we cover". Perhaps not to the degree that you can duplicate the book, or in a way that makes you remember all the technical terms, but all the constructions and how they use them: this is the pace you run through learning Japanese at first year university level.