Not quite, because you can't ignore the density level in the mass equation, & diecast is more dense than plastic. No need to try to cover up for Motuxmen's error.
Nah, I'm not trying to cover up for him, just thought I'd point out there's still usually a correlation between mass and size.
Visually, diecast vs plastic doesn't make that much difference, at least to me. I do see the appeal of diecast in terms of that cold metallic feel, the added durability, and heft. The material itself isn't really necessarily worth more, but I tend to attribute the added cost to possibly a more difficult manufacturing process. However, many of the flaws mentioned by motuxmen is valid, paint doesn't bond as well to diecast as it does to plastic, making diecast more prone to chipping. Furthermore, a lot of times the plastic underneath the paint would be of a similar colour, making scratches less visible.
You make a valid point in that diecast doesn't have to put additional wear on the joints, but like I mentioned in my previous post, to make the customers feel they got their money's worth, the diecast is probably gonna be all over the figure, not just strategically placed. So the increased wear from the use of diecast, especially on a figure of this size, is a fairly legitimate concern.
Between the two materials, it's a trade-off at best. However, between the 2 companies, they chose 2 very different approaches to this figure: different scale, different materials, 1 figure vs. 2 figures, etc... I don't really think there's much sense trying to compare them to each other. For me, personally, with my collection being primarily 1/6th, I'd pick the Hot Toys (if I can afford it), especially since I had absolutely no interest in having a Mark 43 to begin with, due to it being so similar to the Mark 42. The ability to put in a full Mark 43 figure into the HB is a very nice feature for the KA one, but the inability to pose him opened up without shelling out an additional $200 for the Mark 43 is bad. It feels like an incomplete product. If KA was to include a removable bust with the HB, I'd definitely agree it's a better value.
Just thought I'd put it out there, while I enjoy the feeling of cold metal and heft, the cost of these new diecast figures from Hot Toys has become hard to justify (especially with the crappy CAD currency right now), so I'm content with picking up the older plastic versions at a more reasonable price.