Well, there's actually a rank above S. But you can't make any mistakes (Except for expert I assume) while also being fast.
Wow, I didn't really thought of that. But how actually fast you must be?
Beginner: <3 min, 0 mistakes
Novice: <4 min 30 sec, 0 mistakes
Veteran: <7 min 30 sec, 0/1 mistakes (idk)
Expert: <30 min, <3 mistakes
Now I just realized that I am playing minesweeper with casual skill lol
lol x2