Edit: I guess the client also has to run the simulation, never mind. It seems like overall, Factorio is well under-optimized though. For a game that has been out forever, it still has a huge ceiling.
The Factorio devs regularly put out blog posts on the optimisations they have done, like [1][2][3] (and many others), and they have done so for a long time. This gives me the opposite impression.
[1] https://factorio.com/blog/post/fff-322 [2] https://factorio.com/blog/post/fff-281 [3] https://factorio.com/blog/post/fff-209
I know it’s a well optimized piece of software, but when you get into something like the space mod with multiple worlds, where chunks you might not deal with for a long time still tax you, you can see how there’s conceivably a lot that could be done.
So, yeah, wrong to say “under optimized”.
I’m also aware that they haven’t been optimizing for a massive multi-world server with tons of clients. I definitely don’t mean it as a dig or that they aren’t top class.