I've met very very few foreigners here who speak well - and my observation is that those that do are generaly not from English-speaking, or even first world, countries.
I know one US guy who makes veyr few errors, but by and large the foreigners I ave met who are close to prefect are Albanian, Turkish etc - maybe they simply feel they have no choice, but for an Englishmen, society doesn't view you as vermin if you can't speak perfectly.
But it is damn hard - I have taken about 12 courses in all, including repeating levels 1, 3, and 5 at Kielikeskus - something I reccomend doing. The first time the grammar is new and weird, the 2nd time you can start putting it into practice a bit more.
However - I do think this attitude is unhelpful:
think six months working / training in finnish should see you most of the way through from B1/2 to C1, provided a) you understand the grammar and b) you really do use the language.
I think it's fair to say most foreigners will need at least 5 years to reach C1, and 90% never will. I work as a linguist, and I would say very few if my clients will ever reach C1 in English - despite 20 years of speaking the language. Understanding inference, such as puns and allusions, is not a goal one should be thinking of after 2 years study.
I think this is much more realistic:
Within about 3 years I was speaking when I had to. A year or two after that and I didn't need English at all.
That's how it has been for me too.