I'm not with Laminar Research, just a fellow simmer in the UK, but suffice to say that quite a few people have similar issues to you own experiences of low fps. In fact such reports go way back to X-Plane 10 and probably beyond?
Personally however, I've not had the same experiences with the latest 11.31 release, for when I fly over system hungry scenery such as True Earth South, I'm constantly achieving anywhere between 35 & 42 fps. I do suffer from occasional, but very brief drops in fps, although I have always put this down to my PC trying to run other functions in the background, not related to X-Plane 11 itself.
I'm constantly amazed therefore why some people suffer low fps and other don't? It must just be down to all of the various hardware configurations and addons/plugins out there, over and above that supplied with X-Plane 11?
It might be worth submitting a bug report to LR though, just in case?