I have no doubt that some Invision communities are doing "very well" in Google. Some might even say that my site is one of those, however, I can assure you that I've gained at least at least 100,000 in my USA rank (now around 50,000) after dealing with the many speed and SEO issues inherent in the out of the box version of this software. This is a huge difference, and in my case represented the difference between ~100,000 unique monthly visitors before, and ~350,000 after.
So my question to you is, could those communities that are now doing "well" actually be doing a hell of a lot better? Yes.