I was curious, so did a quick check. It's even worse than you describe! I did a comparison between Tokyo->Kyoto (~280mi, ~US$123, 2h18m) and NY->DC (~230mi, US$198, 2h55m). That comes out to $0.44/mi @ ~122mph on the Shinkansen, and $0.86/mi @ ~79mph on the Acela. So the Shinkansen is both cheaper (by almost half!) and faster (1.5x!), even without Amtrak's usual delays and unreliability.

I was in Japan this past summer and took a Shinkansen train from Odawara to Yokohama. It was about 37 miles in 16 minutes, and only cost ~US$18. It felt magical in a way that train travel in the US just can't compete with.