Let me put it to you another way. Here's one of the HT promo pics of the ESB Vader. The version on the left is the original. The version on the right is after I reduced the helmet size by 10%. The white background "halo" is the outline of what the original helmet size was. The way I see it, the helmet reduction makes everything look better. The extended arm even looks less tiny compared to the original, just because the helmet is more properly scaled. A properly-scaled helmet goes a long way in overall figure presentation.
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If that's still not making my point clear, then maybe putting these images next to movie Vader might help.
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And for those who are griping about the nitpicks on these Vader figures, let me ask you this: what type of reputation do you think Hot Toys would have if they routinely screwed up head proportions on every figure the way they do with Vader? The reason Vader gets scrutinized so much is because he's the crown jewel in a lot of people's SW (or general movie) collections. At nearly $300 a pop, it'd be nice to have an HT Vader that looks as convincing as an HT Iron Man, or even a freakin' HT Count Dooku.
HT doesn't need to make a better Vader because every one of them sells out. And then if they came to forums like this one and pop into this thread, they'd see people laughing at the nitpicks and talking about how great their new $300 Vader looks. If I were HT, I probably wouldn't bother trying to make Vader figures more accurate either. What for? The people who raise the criticisms are the ones who get criticized for pointing things out.
With the latest Boba Fett figure, the helmet got changed from the proto - and for the better. Why? Because "minor" inaccuracies on the same level as this Vader were being pointed out instead of just happily accepting another "good enough for me" version. And everyone who bought that Fett is better off for it.