I thought long and hard about answering this post. I'm new to this forum but, I have been using the simulators since about 2002 and I sure don't want to open up a can of worms taking sides on which simulator best represents the real world of train operations. It's a multi faceted question that I will just go ahead and say....none of them do. Yet, each of them have their own redeeming qualities as far as graphics, physics, available content, platform, age, compatibility with operating systems and on and on and on. Each of us will decide what we like.

What real world qualifications do I have to formulate an answer to this post? From the real world side I have been a locomotive engineer and fireman since I was 16 years old so, that's about 40 years.

I am qualified on US diesel and steam having run trains on shortline mostly but also on main lines on occasion. This includes freight and passenger, short trains and long, large locos and small. I also manage series of shortline railroads today. I have been interested in trains my entire life and am one of the lucky (?) ones who turned a hobby into a career that I still enjoy.
As far as the simulation qualifications, I played around with MSTS when it came out. I found I was able to visit the forums and tinker with the physics of that simulator (as guided by some of you chaps that are really good at that sort of thing) and greatly improve the out of the box train simulations. We all know the limitations of that earliest simulator as far as the graphics were concerned and but it was great for the day and the system capabilities. I enjoyed creating scenarios that I felt were real world and trying to cram as much AI traffic as I could into it.. I still visit that sometimes because there are a couple of great routes I enjoy there. Next I decided like most folks to try one of the "better looking" simulators. At the time, about 2012, I decided I liked the looks of the graphics of TS20XX over TRAINZ (don't hurt me Trainz friends

) and tried it out. I love the world assets by comparison and needless to say a lot of the out of the package stuff looked great but, I did find the train physics lacking. An example is a loaded coal train ascending Horseshoe Curve grade at 35 MPH in throttle notch 3. I can't comment on the train physics of TRAINZ because I have not run that simulation. Based on a lot of the videos on YT I see volumes of great content over there and some of it I'm pretty darn jealous of. I've talked to the TRAINZ-ers and heard their reasoning why they might have left TS20XX but, I still find the smoothness and world aspects better in TS20XX. I understand frustrations with world editors and asset creations too.
I also have not tried Run8 but, I have listened to its advocates and hear their reasoning. It has many aspects of the real world incorporated into the simulation including team play (engineer and conductor) ground work. I'll have to leave it to others to comment on loco/train handling physics. I do think that TSW/TS20XX world elements are as good if not better when done properly. Whoops! I forgot TSW. Awesome gaming platform but, needs two or three things to make it better than good ole TS20XX in my >>opinion<<. It desperately needs an option to have your ground man and engineer as two playable characters that you could toggle between, while still running the train from the keyboard controls. This "hoofing it" all over creation to make a cut or apply a handbrake is the worst from a reality standpoint. They should have created a "REMOTE" pack for the Conductor to carry
Please don't take this the wrong way. I think it has the most awesome graphics of any simulator. The sun following the locomotive as it turns on Sand patch and reflecting in the paint or the world reflecting in the paint as you roll along is beyond amazing. I understand also the desire to make it playable across platforms so they get the best bang for their buck but, like many have expressed, it needs a content editor and aftermarket opportunity to be a continued success.
So on to what this is all about.... Simulation versus real world. No, the brakes don't function totally like the real world. Similarly, neither does the tractive effort, sanding effect, or in other words the power applied to pull the train. As the guy in the video shows us about the slack action and power applied and the resultant reaction, the simulator is much more forgiving of sloppy handling than the real world. I can't imagine much success for a simulator in which a novice/newbie tries to run a train and every time he does it breaks apart or derails. Somebody will want their money back! I do realize that even in TS20XX there are parameters built into the programing that will result in consist tilt/derailment under certain conditions. I can't begin to imagine the algorithms and processing required in a true real railroad training simulator to account for weight, grade, drag on curves, rail condition, wheel condition, weather, temperature, tractive effort, rail greasers, and on and on. What no simulator can account for (I suppose, tell me I'm wrong, please) is worn brake shoes, rigging, leaking brake cups, leaky plumbing, two units out of three with bad dynamic brakes or out of sand, and about a couple dozen other elements that can vary trip by trip and day by day. That begs the question "why would you want it to be real?" It can make for a very bad day for certain. That's called a job, I believe. Aren't we doing all this for fun???
So how do I compensate for all of this lack of realism and yet find it fun still?? First, I will say I have never operated a real locomotive or train, over the same territory, that reacted the exact same way another identical locomotive or train acted. Each locomotive, consist, coupled with the territory creates a new operating situation each day/trip. You may drive the same car to work over the same route every day to work but each day can vary, right? So I learn how each locomotive, pulls, brakes and reacts in the simulator as well as real life and compensate on the spot. Big difference.... If I "F" up in the simulator, I load a previous save and start over. In real life, I follow rules, procedures and the little sensor in my rear end, sitting in the seat, to tell me what to do. Braking is tricky in the simulator and obviously much more forgiving. Speed on a grade in real life is unforgiving when speed exceeds the braking effort available. In my own route, which I have been creating in this simulator, I have 2% plus grades that are 3+ miles long with pusher assist. I am happy to say that I find I can operate the simulation almost "real life" as far as controlling the train and operations dictate (and I like real size trains with multiple units and lots of AI). Just like in real life, I learn each locomotive's operating characteristics/physics and run it by the seat of my pants. Yes, there are procedures involved that must be followed in both real life and simulation. BUT I'm having FUN doing it. Isn't that what its all about folks? I see the efforts put into some of these routes like The Powder River, The Bergan, The B&O Mountain Sub and others. I see what can be accomplished. I see how far we have come along from 2012 and it is amazing. I see nothing to really complain about even if I find the physics lacking. We have lots of folks who are creating content and equipment reskins that are great.