They are improving, but mostly individually. From the team perspective only TSM has the playstyle and the consistency over a longer duration to be really a threat to Asian teams.
NA teams always had the problems after 20 minutes that they don't know what to do.
EU on the other hand is knows for their great teamplay with Fnatic and GG. They play their style when they are together like no other team.
So NA needs to be careful, cause they have actually a huge advantage over the EU team in this tournament, an advantage that they won't have when they will clash again with their normal teams.