Where was the testing? After living in Japan I stopped eating sushi in the US. It's always painful when someone asks me to recommend a "good sushi place" here, I'm not sure what to say.
https://medium.com/torodex/salmon-sushi-is-not-a-japanese-in...
Seriously, the sushi places here are on average at least on par with (if not better than) what you'd get from most coastal cities (LA and SF included), and certainly better than what you can find in other "inland" cities, and are almost always all-you-can-eat at a much lower price point than what most coastal cities offer (my favorite here, Tokyo Sushi, even throws in all-you-can-drink sake Monday through Thursday; it ain't great sake, but it does the job).
My hypothesis is that the casinos have built up a strong supply chain for fresh fish (in order to supply their restaurants, including sushi bars) and a talent pool for chefs skilled with handling/preparing fish (including sushi chefs), and independent sushi bars are thus able to piggyback on both. I'm suddenly curious if Vegas has a similar dynamic (I haven't been there enough to know).
Yeah, the rolls and stuff are definitely pretty thoroughly "Americanized", but the nigiri's almost always top-notch wherever I go.