It's not just prizepool.
I feel the main thing that constitutes an S tier among even pro players, is the level of competition.
Like there was a year ago or so in CS, where even pro players didn't see it as a T1/S event because the competition wasn't as good as other events that year.
With who's at this event, I consider it an S tier. the best teams have attended, prizepool is high. The only thing lacking imo is a legacy, and production of the earlier stages were pretty ass, plus having one bo1 then into a bo2. If it was bo2 all the way through until finals, it would be a lot better.