Spin doesn't work against projectiles though.
Regarding the meter building, I do a lot of full screen ice balls, and up close I do F33 a lot. Starts in 9f, -4 on block. Gives you the ability to blow up counter pokes with ex parry, or you can just back dash. Does decent damage and sweet corner carry if it hits.
But there's still a problem, which I think is the only problem Unbreakable has, and it's resulted in buff idea for him; the opponent's meter. That's the only problem with unbreakable for me personally. Unbreakable is designed to block a lot, and that always gives the opponent a shit ton of meter. A lot of times when I open up my opponent they have meter to break, especially if you're playing against a good zoner, which is tiring because you inch your way in and when you get to them they break and you have to do it again.
The buff I want for unbreakable is, when Aura is active, the opponent builds 40 or 50% less meter when Subzero blocks a move. IMO that would be reeeallly good. And for EX Aura, the opponent doesn't build meter at all when Subby blocks.
The projectile parry instant recovery buff has the same goal as my buff suggestion, so I would take either of them.