It's the other way around. ECE standards are meant for lower speed crashes than the American standards. SNELL is the racing standard.
Nevertheless, then comes along someone like (SHARP)[https://sharp.dft.gov.uk/] and performs helmet tests with objective ratings and you see that all helmets vary, regardless of standards.
Because there's no one way to crash, there's hardly one way to test. Buy the most expensive helmet you can afford, more likely than not that it's a better product.
And then you have companies like Arai that have internal standards that arguably exceed SNELL but score low on SHARP due to differences in design criteria.
Because there's no one way to crash, there's hardly one way to test. Buy the most expensive helmet you can afford, more likely than not that it's a better product.