As I just answered in the other question, the font is also transparent (which is hard to see on a screenshot). `compton` (or any other compositor) doesn't distinguish the text from the rest. It simply deals with windows. Thus, that solution only works if you keep a high level of opacity (85% works for me). To have a terminal with a different degree of opacity between the text and the background, this needs to be a feature implemented in the terminal itself, but it may lead to other issues (e.g. with the `ranger` feature you were asking about).
### Update
Good news! True transparency is supported once again in termite, so compton is no longer required for that.