To be honest I see CS more like Tennis rankings.
It is kind of possible to be the best without winning that one title. As there is not really any "season" for cs its just ongoing process where at some point some combination of players can be ranked based on their latest performance. If you had one league people would play for the full year, of course the best would be the one who wins the playoffs that year. Major is still just one tournament, anything can happen.
And remember Keke Rosberg won F1 world championship without winning a single race that season.