Reading is definitely helpful, but I've found the relative importance of reading, listening and speaking goes in cycles, and especially at the early stages, listening and speaking are far more motivating than anything else. And I'm an introvert!
There is no connection between these two sentences. You can learn to read and write in Japanese without ever learning a single kanji, and that's what everybody does do. Kana serve the purpose flawlessly.
Why in the world should any human not from Japan devote limited time and brain capacity learning to read and write Japanese? It's literally a robot's job, at this point.
But isn't this true for most things? It will take a complete beginner years to draw as technically proficiently as an image generation model, or to code as well as Claude. Even before AI, most Japanese media has been available in English translations for years now, and there aren't that many other interests where you could find Japanese speaking peers but not English speaking ones.
If your goal in life is to generate the most economic value per unit of time input, maybe then learning to draw, code, or speak Japanese no longer makes sense. And if that's your priority, you won't choose to do these things. But that's not why people take up these pursuits. So I don't think AI will have a huge impact on how many people start them.
In an ideal world maybe learners could focus exclusively on listening and speaking first, then move on to kanji later. But writing is a very useful tool in learning, and having access to that tool can help speed things up.
Like most things in life, a balanced approach is probably the right one. But you have to know what your goal is. Our brains are lazy, they only get better at what we make them get better at. If your goal is to just read kanji, practice reading kanji. If your goal is to understand and speak the language, practice listening to and speaking the language. But if you want to have a balanced language ability, you'll need to practice it all.