The LaTeX input for Word equation editor makes it a lot faster, but it is still quite limited and often doesn't do what you expect for more complicated things. It makes the easy things easier, but the hard things harder.

...no, you can't. Sure, for a few one liners it works OK, but it's not like an embedded latex environment. At all. I've used it extensively.

As far as speed, even for simple stuff the real time formatting gets in the way constantly compared to just writing text in a latex file.