I had to return that game because it was totally unplayable on a 2009 iMac with Radeon 5850. That should be plenty of computer but there's this obnoxious cloud simulation over the top of everything that pegs the GPU. Pretty sad.
Skylines came out only this year. 6 years is a long time in the gaming world. I wouldn't expect to play many games from this year on any computer from 2009.
That could potentially run on a Pentium 4 with integrated graphics, not exactly the best comparison. Great game, but not sure why you felt you needed to include it in that list.
Quite a few of those games are not overly demanding either and mostly forgiving of older graphics cards. If you can run things like Arma 3, Witcher 2 or 3, I'd be more curious.
Cities Skylines is a simulation, it's going to eat up a lot of CPU and a lesser extent, GPU.
If Bohemia Interactive wrote ARMA 3, I wouldn't take its requirements for a beefy machine as indication of anything other than the... interesting design choices those guys make when designing and implementing their games.
I run many, many, many recently released (and not-yet-released) big-name 3D games on 5 [0] and 6 [1] year old hardware.
Console-first development has done terrible things to video game design, but it has let cheap bastards like myself get enormous mileage out of our gaming rigs.
(BTW: Cities runs juuuuuuuuust fine on my "ancient" PC. :) )
[0] Radeon HD 6950
[1] AMD Phenom II X4 955