Ill throw in my two cents on R1 Vader....
Ill start off by saying that I LOATH ROTS Vader and I put R1 below him. Here is why I feel that way.
All 4 of the other Vader's are actually well proportioned and balanced in look and build. R1 is not. The whole shape and silhouette is wrong. Biggest thing that throws it off is the helmet is far to low. No I am not talking about the positioning of the dome, I'm talking about the entire helmet being too low which actually makes Vader look like some buff guy who worked out to the point his chest swallowed his neck. Spencer is pretty darn big and has a nice build yet he looked very thin in the suit, to the point where the big Prowse look was thrown out the window.
And lets talk the helmet. This is the poorest and most pathetic piece to come from an official Lucasfilm Production. The face is the freaking Quasimodo. Mac has stated that himself on the RPF and I see it my self. The crew had access to the archives, the original helmets and the Rick Baker mold but instead used a fan sculpted face. One that has little to no lineage to the original helmets. That is sad Very sad. In my opinion the Quasi's features are way to exaggerated and the cheeks slope down too much. I have yet to hear the source for the dome. The last thing with the helmet is the neck, why did they extend the neck? It sticks out like 10 feet away from the armor and at times I can see a gap between the neck and the armor, more soo then we ever see in the OT.
The armor and the cape are the next 2 pieces that are bad. The armor takes after the GT with the chest plate flaring out wards and it also looks undersized. Yes I find it really noticeable that it is undersized. The cape is just horrid. They used way to freakin much material on it to the point where it covers 90% of the armor and front of Vader. The original capes were 4 panels at a half circle but I believe they used 6 panels. That is far too much material in order to achieve the right look. The material itself looks cheap AND they hemmed it far to short as I could see the back of Vader's legs.
Cod piece is just garbage.
The suit gloves, chest box and belt look good. Well the belt and the chest box are spot on for ANH Vader and I believe that is due to the fact that the crew didn't make them. They were provided if I have my facts correct.
Overall this version of vader looks like some guy trying to gain basic access to the 501st as ANH Vader. We as the fans have developed much better suits and its hard to believe that thing came from Lucasfilm. I would rather them not include Vader in any future film if that is what they will continue to use.
My opinion comes from the fact that Vader is my all time favorite fictional character created by the minds of mankind.
It's been a very busy year, and I've been catching up on some reading, and have been late in responding.
I appreciate you trying to be the authoritative voice of what's wrong with Quasimodo or the Rogue One Vader. Here are some points you've overlooked and supporting screenshot analysis that anyone can decide on without bias.
Regarding the issue of the neck allegedly sticking out "10 feet", one thing that has been overlooked in this thread is the symbiosis of the neck and armor that must take place in order for the helmet to not only rest on the armor properly but the setup to appear anatomically correct. If the armor is misshapen, it cannot support the neck properly. The armor is no more a screen source than the helmet, cod, and other parts are.
These comparisons show the front chest angle to plunge too steeply, causing a significant neck gap, and there is a massive hunched-back look which will cause the neck to not sit properly on the armor. In short, the two costume parts are of different makes and weren't made in symbiosis for each other.
In the above, notice the first two (ESB) screenshots show a particular front-to-back chest depth and, accordingly, front chest angle. The back is not hunched. By comparison, the Rogue One does not exhibit the right shape. As you may recall, Brian Muir sculpted the original mask and armor over a body casting of Dave Prowse so that they would be structurally in symbiosis with each other. Conversely, the Rogue One clearly does not exhibit that symbiosis.
In fact, the issues are similar to what I've pointed out in the following infographic ("Large Neck Gap") I've shared regarding Quasimodo and its Structurally Matching Armor:
In the next image, let's study the mask's neck issue I've also included a sideshot from a second or so before, and how the neck does not stick out "10 feet" a moment before!
Again, notice the hunched back and the plunging angle of the front chest. Despite this, the neck of the mask does not appear to stick out 10 feet as you say. With some brightening, we can see the armor is clearly warped and inconsistent in shape with the screenused original trilogy armor. Like in my infographic on warped armor and ill fitting, you can sometimes win by making the front look good, but you sacrifice the back - or how it looks overall from the sides.
Also, note that Krennic has crumpled onto the floor. If you rewatch the movie, you'll notice for a split second that Vader is very slightly tilting his head slightly in Krennic's direction as Vader turns. The armor, which was poorly supporting the neck, is now not supporting it at all based on its shape.
Here is an additional look at the armor and its hunchback shape - a corroboration from the Blu Ray "behind the scenes" footage (right, brightened) in comparison with the ESB (left):
Here you can see the hunchback effect with the Rogue One armor. There is significantly less space between where the flange silhouette ends and the armor's trapezius begins. For some reason, I find this to be more of an issue on the actor's left side.
To conclude, here are the potential dimensional differences between the armors:
Under these circumstances, I cannot say that the armor here was GT, nor that it was too small, nor that Quasimodo's neck was modified or sticks out by the alleged 10 feet. The armor has the "feel" of a fanmade, which reinforces the many observations and suggestions of not only fan-sourced Vader costume parts but other props (such as the Death Star Droid) as well.