Hm, that's measuring everyone against the same dollar; Americans are productive by this measure because everything is expensive. I wonder if there are other benchmarks for productivity, adjusted for local market basket.
Although there doesn't seem to be any obvious evidence here that the US could be lagging behind. Per-person the US is still a bit of a productivity outlier to the upside. When they aren't legislatively restrained they tend to work hard and in an organised way.