Yes, because the alternative is racism.
I mean, I know asian work cultures are "harder" than my european one, but is it incorrect to spell that in a public/social context?
It's not insufficient data, it's uncharacterized data.
If more-or-less everyone with exposure to both cultures is in broad agreement about the differences, that's not "insufficient". It's probably actually more data than any formal study would generate.
But it's also lower-quality data, with a greater chance of being distorted by various cognitive biases. Which means that it doesn't meet current regulatory standards[1] for use on large protected-class[2] groups of humans.
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[1] as loosely and collectively defined by the morality police, loudest / most extreme non-ignorable activists, Internet Lynch Mob, etc
[2] which includes pretty much anything these days
To your point, a better title might refer to "Asian Countries" and "European Countries" instead of individuals. Europeans living in Japanese companies work similar days/hours as their coworkers, of course.
It's a social study, not geography. Assuming that Japanese are like that or french people are like that is indeed prejudice, since there is no data to back things up but individual bias, or bias promoted by movies or the pop culture.
I agree with your second point.
"According to the study, South Korea and Japan lead the legions of overworked...On the other side of the globe, workers in Finland, France, Germany and Spain are all given 30 days of vacation each year"