These last two posts by Merranvo and Skalex hit the nail on the head.
Lees and TGC knows where the problems occur. If you followed Lees diaries when FPSC was being developed you would have seen exactly the issues that Lee struggled with to boost speeds and find solutions to those issues that cause slow speeds and fps issues as the issues were clearly spelled out for all to see.
Some of those issues were apparently never completely fixed or overcome - but only partly so, and in some instances improvements were made.
Issues in the main and understated as they are complex issues were related to :
Dynamic entity AI think time drains or losses.
General optimisation and particularly an unknown issue which causes the unecessarily high dropoff of fps or serious Lagg issue in small specific locations.
We now have an idea of course why this is happening - "culling and overly high poly counts" - though not perhaps all of the exact underlying reasons.
These are the two main reasons and they have an influence one upon the other - together they can cause some serious problems with fps.
This irrespective of the fact that FPSC is no doubt not the fastest underlying engine design in the world even given no speed bugs or issues.
Quote: "All the professional games and most of the amateur games have optimized levels (unseen polygons removed)."
That goes for engines too. I dont know of any other indie engine that ignores poly reduction in compile that has been released for sale as a complete finished product. One would normally expect such to be a Beta Release or at least a promise that such an issue would be under development for fix inclusion in a future release as might be other issues or features. I am probably incorrect there mind you as I dont know every engine and I dont follow so many these days.
If its true that FPSC ignores or does not carry out BSP level optimisation during compile - then I presume the BPS renderer is faulty. If that was known by TGC I cannot understand why that was never specifically referred to as far as I can recall during development of FPSC - though again I did not read or follow all information published.