Question1:
Does any character have a response to multishine shield pressure other than a frame perfect samus up B?
I am inclined to believe that they don't.
Question2:
If not, why ever do anything other than multishine on shield?
Question3:
Why not just immediately JC shine grab (as in approaching with falling aerial on shield->shine->grab) rather than doing whatever else?
In theory, multishine shield pressure pretty much leads to shield break. It's just that most people can't do more than 3-4 in a row
fast enough to keep them in hitstun.
As for question 3: It's about mix-ups. Every shield pressure option has answers. Early shffl aerial --> shine gives them a small opportunity to shield grab/attack you before the shine comes out, if they're paying attention. Or maybe I'm just slow.
Late aerial --> shine gives them waay less chance to respond to the aerial --> shine; however, if they know you're gonna late nair or something, they can hit you before you attack.
Shine --> Grab is good when opponents like to hold their shield a little longer after your initial barrage. But it comes with its own holes and defects. Idk, wavedash out before grab and hit you when you whiff...or hit you before the grab connects. *shrugs*
And there are plenty of other scenarios and shield pressure options. That's why it's good to mix things up.