Guys, the problem with the franchise is not lower/higher graphics. As you said, Cities Skylines was much bigger than Simcity and it didnt lag, didnt crashed... The problem with it is that EA gives a really short amount of time for the devs to work, they hav to rush to create the game, which means too many bugs in the release and usually heavy games (like sims 3).
I mentioned the graphics, because I remember Rosemow once said that the open world in The Sims 3 caused many graphics cards to burn. I play Cities: Skylines very smooth and with no problems, even now when I have a large city, with so many citizens and vehicles moving around and doing things. I can't tell what was the exact problem that the cities in The SimCity 2013 were so limited in size, and that there are loading screens in The Sims 4. At least the neighborhoods could have been open, but I have a very laggy and stucked gameplay when playing with a large house even on a 30x20 lot, and a 64x64 lot becomes unplayable after few days. If it's not for heavy graphics, then it could be for the large number of objects in use and their functions, or for inefficient and massive code.