For me there are pluses and minuses with both of them,the eyes,nose and neck look better on the kaiyodo but the cheeks,mouth vent and neck bulge look better on HT and they got the mouth/vent crooked too! And the dome looks to have been scanned down from the original as it's wonderfully wonky and crooked ..just superb.
You are right man! About the facemask I've to say that the minus of kaiyodo are really little noticeable. (hurricane facemamask seems near perfections) Ht facemask is weird even if there are little imperfections. About the dome, nothing to add to your words, ht is really near perfections even if I'd like to see ht dome on Hurricane facemask ( if they are in the same scale) for the final judgment.
The thing that to my eye looks most off with the HT is when you look at the higher angle, the eyes are sloped backward just slightly too much, giving it that cat/feminine or McQ Vader look seen more clearly in the proto. Even though it's still not 100% accurate either, you can see the Kaiyodo eyes are flatter. I also think the Kaiyodo neck looks broader and more accurate, though HT Vader is a bit skinny overall, so it's not too noticeable on the figure. The HT button nose does look a little odd/deep in some pics, but looks good in most.
I thought the same thing when I got my Kaiyodo kit (a bit shocked actually ) but I think it was Too Much Garlic who said the dimensions of the Kaiyodo exactly match the screen used helmet in 1/6. I did quite a bit of research because it just seemed wrong, especially next to the HT Stormie helmet but eventually found a jkno pic that showed the two replica 1/1 helmets and the props were similarly scaled. But as I mentioned earlier, what the comps showed was that it's the SSC DX dome that make the Kaiyodo look too small - a modded SSC DX is the most commonly used on the Hurricanes (Matrix used it too) and it's 10% too small and the skirt also flares out a little too wide.
If you have a close look at the HT vs Kaiyodo, the facemask dimensions (tusk-tusk, outer cheek-cheek etc.) they are about the same on both, whereas the Ht dome is noticeably bigger.
This is the kind of conversation that makes me feel less alone! Thanks TaliBane for your Star Wars accuracy!