Their methodology is briefly described here: https://www.topuniversities.com/qs-world-university-rankings...

So, the proportion of international students and faculty (which account for 20% of the rankings) will massively bias the rankings towards English speaking universities, because more people study abroad in English.

Additionally, the academic & employer surveys are biased by the fact that name recognition is much, much higher for older universities, so it's likely that they will be perceived as being better in the absence of any real differences.

Nonetheless, when people say that Finland has the best education system in the world, they are referring to the OECD data. You're the one trying to use university rankings as a proxy for this, when it should be clear that primary & secondary education are much more important from a population perspective.

Additionally, students in Finnish universities are paid to be there, and may also be provided with housing. That's a much better deal than one would get at Oxford/Cambridge/MIT.