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.
https://scontent.fsnc1-1.fna.fbcdn....=9171fcc09fbcef3e34775626679c0f75&oe=5AC338F1
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:
https://scontent.fsnc1-1.fna.fbcdn....=3dbefb81a30a0285af8d0a4dd18a15a7&oe=5ACB70E2
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!
https://scontent.fsnc1-1.fna.fbcdn....=4978bfe29c70249d8c29ca2544826c8b&oe=5AB61B25
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):
https://scontent.fsnc1-1.fna.fbcdn....=f1537ff008799c8786f6ec43ace74253&oe=5AB73FE2
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:
https://scontent.fsnc1-1.fna.fbcdn....=2d87134c6aed8294cdc647b43fa46499&oe=5AF67B74
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.