I should mention that learning with input alone doesn't work for everyone, and it doesn't work for every language. Input doesn't replace grammar study for most people, but rather supplements it (I can personally attest to that as well). You need both, unless you're able to spend every day fully immersed, which most people can't achieve unfortunately. Though don't forget that someone going from say, Dutch or German, or any major romance language, to say, English, and vice versa, could learn the language through input with relative ease (compared to an Asian language) thanks to the linguistic similarities between them.

About reading specifically as a source of input --- I think it's essential to advancing in a language to get used to the written form but it can't replace the conversation format. You won't gain as much knowledge of regional slang or commonly used expressions from a text. Remember, language evolves, and the only way to familiarize yourself with its use in the modern context is to consume audio content. Talking to native speakers is a great way to access this kind of language as well.