Obviously I can't give specific suggestions since I don't know the ins-and-outs of their code or engine. Maybe they forgot to turn on compiler optimization flags again, who knows?
Well, as an educated guess, changing some compiler flags isn't going to give you an extra 5 frames when you have a dynamic light casting over a high traffic area. Dynamic lights are very expensive, especially when they're lighting lots of moving objects at the same time.
The point I'm getting at is they aren't idiots, they know what the engine's limitations are, and this was clearly going beyond it's limits. This is not the fault of the engine, this is a fault of whoever placed that light and made it dynamic in the first place.