You'll be wise to ignore Redditors when they claim to be making some kind of breakthrough that eluded professional game developers over years of development.
In another comment there was a link to https://twitter.com/AtkosKhan/status/1717525097626349696?s=2... with a note that it can increase FPS by 100% by just removing cim rendering using the game's developer mode, so it *does* seem like cim rendering does have major impact in the game performance, if you have cims to begin with :).
edit: Curious coincidence though that there are LOD improvements in the C:S2 hotfix released yesterday: https://forum.paradoxplaza.com/forum/threads/patch-notes-for...
https://www.videogamer.com/news/cities-skylines-2-teeth-perf...
> “Citizen lifepath feature does not tie to citizen geometry and does not affect the performance figures of the characters. We know the characters require further work, as they are currently missing their LODs which affect some parts of performance. We are working on bringing these to the game along general LODs improvements across all game assets. Characters feature a lot of details that, while seemingly unnecessary now, will become relevant in the future of the project.“
So I guess sometimes these things can elude professional game developers over years of development.