As much as I'd like to agree, winning the Major shouldn't automatically result in that team being #1. Cloud9 won a Major and never rose above #2. Gambit won a Major and never got close to #1. NiP won their only Major a year after they were #1, and weren't ranked #1 after they won it.
I think winning a Major goes a long way towards making an argument, but itself shouldn't be a determination on who the #1 team is. #1 at a tournament? Sure. One of the 3 biggest tournaments of the year (if you include Cologne, which actually has the toughest competition of the year this year, and which Liquid happened to win).