Framerate drops is the result of poor optimization/overestimating hardware's capabilities, Forza 6 runs at 1080p/60fps locked at ALL times with no drops because T10 specifically optimized for that target despite having weaker hardware than what PS4 offers. It's a design decision by the developers to juggle eye candy/framerate ratio as they please. You could give developers a system 100 times more powerful than PS4 and you would still see framerate drops if they wanted.
I'm still in the learning process on much of this stuff, so I know I'm wrong on a lot of these things. I do know without a doubt though that the PS4 was outdated before it came out. But you're right, it's no excuse to have frame rate drop for the prettiest game at fleeing moments while the rest of the game tears, shows it's jagged edges, and lags behind due to poor programming.
It isn't that, it is the fact that with other sims out there offering incredible realism features it is a joke for PD to offer something featureless. iRacing doesn't have 2 of those 4 features he is requesting and it wasn't the first for any of them. The features it has are better than other sims IMO but there are plenty of sims offering some sort of dynamic track, pitlane limiters and rain and much more.
In my opinion in 2016 what PD has shown us is an arcade game and no longer worthy of being called a sim. I know the term simcade is thrown around a bit but you can't call yourself a sim any more if you are not even trying to do some type of realistic damage or collision model. To call what we have seen a sim is like calling any arcade racer a sim as they are all imitating driving or racing. But I think to fall into the category of simulation in 2016 you need to be trying to simulate racing with modern features that modern hardware is capable of. You must at least be trying to simulate weather or changing track conditions and realistic physics including collisions and consequences. I'm not saying a sim must have every feature out there but they should be trying to simulate as close as they are able racing a car and to me it doesn't seem like GT is trying to do this. It seems like these guys don't know how to do these things and they are milking a name for all it is worth.
Very true PD and the GT franchise is so far behind today than it ever was. First games in the GT series used 3D imaging for cars with a simple physics model attached. Now that they have to create actual 3D models, they are making excuses as to why they can't make premium cars. Hence why the Standard models looked like crap; they were ported images from previous iterations of GT. As for features, they do lag behind there as well. I don't think they will have pitlane limiter or much of the other features like iRacer, but the physics part they are falling horrifically behind in. GT6 was a complete flop in the physics and tuning departments, as in many others, but I would say the Physics part took top prize in that battle. The main thing is, I don't think PD is trying to add new features but rather make a realistic handling model per their claim, "The Real Driving Simulator." It's sad, but it seems to be the only thing they are focused on. I know I sound like a lone wolf here, but I was really hoping for the drivetrain and motor conversions and swaps. They added Jay Leno's Toronado which had a Drivetrain conversion AND a crate Caddy motor, but condemned players who made their own. If they added that feature, they would at least be a bit more on par with Forza, but again as you said, they haven't added much features, if any. Just a revamp of a couple and a livery editor.
I think the tracks need a major overhaul too. The Nurburgring videos were very disheartening. The track seemed to have had about as much detail as any other GT title. On the other hand, Need For Speed Shift 2 and other simulation titles had a very detailed Nurb with many individual trees, tents, moving spectators, and so on. All of the GT games have had poor surroundings and this game didn't seem to change much more. I can only hope GT7 will be much further advanced than GT Sport/Gran Turismo 7 Prologue is now.
Like I've said before, I haven't a problem waiting years for a good game, but within those years, I expect the finished product to look excellent and to exceed other titles at the same time. It's been done before, so there is no excuse as to why it cannot be done again.