I’ve been to a few sushi buffets in Helsinki and I can guarantee it wasn’t surimi after googling to see what that would look like. It was almost entirely salmon and tuna.

That may be the case and I don't doubt your view, but you'd be surprised at how good the Surimi manufacturers are at producing "sushi analogs" these days ..

I doubt surimi can ever approximate a slice of tuna or salmon, even if it's hidden in a maki roll.

California roll 'crab' yes.

I assume crab rolls are a good target for that stuff?

Indeed.