STK
Beso de Muerte + Fantasía Oscura
what moves do you need to punish with exspin that you cant catch with b321 or f2?...What? I don't understand what you mean. You can't do the same thing with EX hat spin because the moves are not comparable.
EX spin in Buzz Saw is used to combo punish things and anti-air because it's so fast and covers a great distance. It's 7 frames and that is much faster than any of Kung Lao's other combo starters.
EX hat spin in tempest is not a punisher and it is not used during combos, it is used for block pressure and frame traps.
One is a fast punisher and the other is used for pressure. You can't compare them when deciding on which variation to use because they fulfil completely different roles.