Didn't they just win a tournament against all the top teams? Not only that, they trashed them. It is a valid argument that astralis is performing the best atm. Not to say other teams won't bounce back. But looking at this tournament it does seem like it.
It doesn't make them the best the next 5-6 months, no. But since there is no clear top 1 and every other team, other than astralis, seems to have some form of issue, I'd say it's a valid argument non the less.