1) You run latex twice only on really large and complex documents like books, and if you're writing books (not editing, see antipope.org for details) in Word, then you need professional help.
2) Markdown and LaTeX are designed for different tasks. Next you'll be telling me that if you have a leafblower, you have no need for a chainsaw.
3) Find me the structured and annotated data streams first - and show me that the structure and annotations are correct - then lament the lack of a shell that can route them to the programs that don't interpret stdin and stdout and stderr that way anyway.
4) I use vim to write latex when I write latex, but "in a bash shell" doesn't make any sense. You fire up vim from bash, yes, but unless you're trying to do an ex-style editing session, you're not editing in the shell any more than you're editing in the kernel or the tty driver...