As a SMN, I wouldn't be worried about BLM catching my ST DPS in a stand-up fight, or a movement heavy fight like Titan Ex. This change to surecast would be good, but unless the non-traited version allowed for movement while casting, it would be more or less worthless to everyone but THM/BLM, which is kind of pointless for a cross-class ability.

If the traited version allowed for significantly more casts to go through during the duration of the spell (i.e. 8 -> 16 or 6 -> 12), that should be enough benefit to make it useful for everyone, but more useful for THM/BLM. But if the un-traited version didn't allow for movement, it would be as useless as a cross-class skill as it is now.