WK won’t teach you lots of things you need for that:
- Listening skills
- Vocabulary (it teaches a lot, but only in the service of helping you memorize kanji)
- Cultural knowledge (necessary for reading or understanding some materials)
You didn’t say what your native language is, but Japanese is difficult because it is quite different from most other languages (except Korean). See Japonic languages:
… more attempts have been made to link Japanese with other language families than for any other language. None of these attempts has succeeded in demonstrating a common descent for Japonic and any other language family
So unless your native language was one that is vastly different from English, your experience of gaining fluency in English may be misleading (Japanese will be harder).
In addition, there is the challenge of the writing system, which WK will definitely help you learn.
You can burn everything in WK in 2-5 years, depending upon how much time you put into it. But you can find people here on WK forums who have reached level 60 and relate that they have poor listening skills, or that they have not yet progressed beyond JLPT Level 3.
That said, if you also gain enough grammar and listening skills, you should be able to consume Japanese material (with some difficulty) after level 40 or so.
There are book clubs here on WK forums for readers at various levels (but even “advanced” here is not that advanced; they read slowly, and the materials they choose are limited.
All that said, I suspect it will take more than a certain number of months for you to be able to consume original japanese materials. Two years would be fast.
There are two aspects of learning Japanese as a second language that are easier than most other languages:
- it is phonetically simple, and therefore pronunciation is relatively simple
- it has extremely few grammatical exceptions