It's a good question to ask. Characters like Liu Kang and Mileena can still break armor I believe, despite frost bomb being pretty fast (15f). There are strings designed to do that, but frost bomb is better than crushing hammer (28f) for sure, and harder to punish than (9f) icy slide if blocked.
Cryomancer has armor breaking strings of his own after any hammer HKD into jip, 1 strings (success @ 19f) beating D'Vorah's options. Or simply 11 on opponents wake up (success @ 11f) beating Erron Black's options.
A lot of players get confused when their wake ups don't work out because they don't know the limitations of their armor. Sub has the luxury of possessing one of the best back dashes in the game to lean of when armor is risky.