What is a space sim for you ? We don't seem to have the same definition of it (I don't say my definition is the good one).
I'll just get that one (there are quite a few other possible quotes here): Kerbal Space Program is a pure space sim. Here, you have the true feeling of space. Yes, you do have EVA, seamless planetary transitions, etc. AND pure newtonian mechanics. I could name a few others, going back to Amiga games actually (Frontier, etc.), but that one stands out. This is what defines a "sim",
simulation. Otherwise we are talking about arcade games, which is an entirely different subject matter.
SC is lacking a proper physical model at the moment, the ships movement is goal-based and not inferred from newtonian physics. There is no simulation. It feels like dragging assets in a 3D editor, not like flying a space ship. I reserve my opinion on the atmo model until 3.10 pops out in the next few weeks as it's been redone, but until now, there was nothing to be said about it. Again, KSP (with a mod called "Ferram Aerospace Research") had a terrific atmo flight model, with all subsonic and supersonic effects. And that was developed by a team of how many, 5 ? And the mod done by a single guy. Let's compare this with the $300 million project from CiG with a 500 person strong team...
(edit) before the usual zealots answer with "but it's not supposed to have orbital mechanics !!!! orbital mechanics not fun !!" first i have never said that, i would just mention that CiG themselves advertised "True Newtonian Mechanics !" for pages with a huge amount of details on 2nd and 3rd order movement etc. back then in 2012-2014. I would certainly not expect a fully orbital sim but at least have proper scaling of thrusters on ships and the according reactions to movements, and proper inertia and accelerations. At the moment the ships exhibit instant infinite accelerations when changing directions.