Some of the addons, like the FIRS industrial economy are quite complex and it can be tricky to assess or estimate optimal routes/investment.

(Feels a bit soon to repost somehow…)

If you have 4 real cores, with 2 hyperthreads, the system reports 8 CPUs. But that's fake. Hyperthreads share most of their compute and register resources, so they only work well if a core is spending most of its time waiting. 2 hyperthreads both doing full compute will basically work at half speed each, which is close to what your graph is showing.

BTW, you can check on Linux with this command LANG=C lscpu and checking the Thread(s) per core value

But I since found that 4 are “efficiency” cores, so that could be the reason for the poor scaling(?)

There was only one I could find: "exploring the performance of trAIns". I looked at the "trAIns" link and cannot understand what it does, other than being GPL licensed.

It's all very cryptic, without any explanations. To me that stands for "if you don't know already, you need not apply". Too bad.