I haven't experienced anything to the severity you have described in Limsa. Sure, there's a bit of an fps drop while zoning in during prime time. But it's nothing too crazy. The Firmament on day 1 of 5.2 launch though? Now THAT was a lot of people, and it was certainly worse than anything Limsa could throw at me. But...I still had no problem moving around and getting things done. It was just at a little under half the frame rate I'm used to. It has since eased up a bit as people lose their interest.