While on the other hand, I use it because I can open a shell from within Emacs.

I can also use tramp to ssh onto another machine from within emacs, and so don't have to bother installing my favourite editor on headless servers and Raspberry Pis.

Is there a true terminal inside emacs that I don't know about, because all the ones I've tried were buggy chimeras of odd behaviours.

`ansi-term` works well in most cases. The only time it really breaks down for me is when I run commands that combine really long lines and complex escape sequences (like npm's new progress bar which you can thankfully disable).

I'm quite content with shell-mode for most of the things I do (took me a while to get used to some of its quirks, but now I like them). For curses applications (like alsamixer) I use ansi-term.