The 9.3X64 is superb, but I expect US Gun makers do not make any because they believe (maybe rightfully) that the 9.3X64 would never sell sitting next to a 375H&H.

I think they are wrong, but I have to admit, it would be a gamble. The ammo makers (and brass makers) are probably the real issue here. Most of the existing US made rifles can be easily reworked to feed the big 9.3, so the guns are not a problem, but getting someone to commit to tool up for the cases may be a gamble they just do not want to take. The logic would run something like this:

The 375 does it all, and has done so very well on the US market since Winchester first chambered it in their M70. So to get the same performance in a new-to-our-market cartridge is not worth the gamble.

Still I like the big 9.3 because it does what the 375 will do, and can be made to hold 1-2 more rounds in the mag and requires less work to modify an action and bolt fact to use it too. I have used the 375 a lot, and I have zero bad to say about it. So saying another shell will give the same results is very high praise in my mind.
I have seen the 9.3X62 used quite a few times in the last 8-9 years and I have shot a few round myself from that shell, and I have personally used the 9.3X74R a lot more, and seen excellent results when I use good bullets. The 9.3X64 beats both of these shells by about 100-200 FPS, so again, given bullet that will not shatter, I am 100% sure it would be excellent because to be perfectly frank, I can't see a lot of difference in the kills from a 375H&H, a 9.3X62 and a 9.3X74R, so I see no reason the 9.3X64 would not be as good.