Oh, it will be subtle to most. But for me, it's the only thing that could get me to keep the figure. Each little mod I do to the shoulders goes a tiny bit further to make it look like a normally proportioned man in a suit.
Not to be judgemental but I think of all your problems with the figure in your video the tummy one I found the most It was difficult for me to see a problem there.
Back to the head though - I think its too small rather than the shoulders being too wide. When the endoskeleton came out shorter than the Enterbay Terminator figures I thought it was perhaps due to the endoskeleton design in real life not corresponding very well to a normal human physique and Hot Toys weren't to blame for that. Then Hot Toys released this Batman and he too came out shorter than the Enterbay figures. So that made me go back on the endoskeleton and realise, no, he's shorter just because that is what Hot Toys have decided 1:4 scale should be, no other reason. And I think likewise with the size of the heads, HT have simply decided 'this is how big we'll make the heads on our 1:4 scalers'. That little bit smaller. The endo has a pretty narrow head.
Having said that you're right, when you can't do anything about the head size, do something about the shoulders instead.