To be fair, SC5 was released in 2013, and it did run, didn't it?
I mean, aside from the servers capacity issue (the requirement of which was patched out quite soon), the min specs were something like 2 GHz CPU, 2 GB RAM and 256 MB VRAM and the DLC was quite an expansion, turning it all futuristic, including MegaTowers. Or they sure could have increased the size of the districts, and by it also the HW requirements.
As for CS2, I tried it over Xbox Game Pass, and I don't have any stutter or lag even in a 100k city (I downloaded a save of). It feels quite bland though, reminding me of Cities XXL. There, the maps are quite large, but one just ends up zoning the same over and over again - albeit there was at least the possibility to have trade between several cities one built, such as a city with plenty of farms, which then supplied the other cities.
Not that CS2 seems all bad. I.e. there is a broader take on industry and commerce than before, and some other niceties. But as is, having plenty of squares of one-family homes near huge industry buildings, somewhat weird - and when one gets to unlock some more squares to build several villages on the outskirts, their taxes don't easily pay for all them big public service buildings - and stuff like that.