I've used those apps and the problem is that they only support a tiny subset of the format, and they can't support any of the features that require the rest of emacs to be present which is a lot of of the value.

If you're okay with the stripped down version that's basically markdown but different and that's fine but I feel like most people fall in love with org mode because it's so powerful once you get it going and all that power comes from emacs. So I get the argument that it's no worse than markdown but you lose so much of the magic.