[thaumasiotes]

I mainly use my phone for three things:

1. Pleco

2. Wechat

3. Kindle app

Pleco (a dictionary) and Kindle (an ebook reader) work fine offline. Why wouldn't they?

Wechat, of course, can't do anything offline, because it's communication software. It is not even clear what "use wechat offline" would mean.

Android itself obviously works equally well whether you're connected to the Internet or not. What do you mean by becoming "almost a brick"?