A is better because it replaces all forms of defensive tactics. Why roll? Rest has 20-something frames of invincibility and auto-deaths them if they're not spaced, making it strictly superior to sidestep, and frequently superior to shielding, rolling, WD oos, etc.
It also automatically shield breaks, and forms ridiculous offstage combos.
If you can JC it on frame 1 you can double Rest for instant KO.
It's strictly better.
Shine doesn't help ICs that much. They can set up better, but ICs with Shine doesn't beat everything in the game through invincibility abuse and instant KOs in the same way that a JCable Rest does. It's a parry, death combo, superior sidestep, and several other things all at once. That's too much versatility and it covers too many things.
ICs with Shine have the limitation of the single frame of invincibility, the low range, the fact that ICs aren't mobile in the air, the execution demand of something like that, and the low shield stun of the Shine. And other things. Plus the Shine just knocks down some characters. Which makes it non-guaranteed as an automatic stock.