It never really was an argument to begin with for any neutral observer. EU was clearly superior until the end of Season 5. They only season where NA teams got better results was S4. This year NA looked a bit stronger imo but in the end EU still made the Semis while NA didnt get past quarters once again.
If you look at past results NA vs EU is not really a thing...NA fans like to discredit Season 1 worlds so I am not even counting that but even if you look from Season 2 onwards only it is not close.
Season 2: EU 2 teams in Semifinals (Moscow 5 and CLG.EU) | NA 1 team a quarterfinals but only cause of a group bye
Season 3: EU 1 team in quarterfinals, 1 team in Semifinals | NA 1 team in quarterfinals but only cause of group bye again
Season 4: EU 0 teams in knockout stage | NA 2 teams in quarterfinals
Season 5: EU 2 teams in semifinals | NA 0 teams in knockout stage
Season 6: EU 1 team in semifinals | NA 1 team in quarterfinals.
So since Season 2 EU has had 6 semifinalists whereas NA had 0.
6 EU teams made it out of groups while 3 of them finished first. Only 3 NA teams have ever made it out of groups and none of them finished first.