Surecast is one of those cross class abilities that plays a very niche role.

I only ever use it when i know that there is incoming unavoidable damage, which will cancel my next spell cast. Even then its not overly useful and feels like a wasted spell.

----- suggested change ------

In order to improve this spell and make it a commonly used cross class ability the spell should be changed from;

Next spell is cast without interruption.

to

Next spell is guaranteed to be a critical strike.

Having a guaranteed critical strike would be all sorts of useful, the guaranteed burst for black mages would be amazing on things like conflags, gaols and any add that needs to be bursted down quickly, same goes for summoners with fester.

Having a guaranteed crit adlo on scholars or crit medica or cure 2 on whm would be amazing, to prevent spike damage or recover from a harsh aoe/burst damage on tank.

The improved surecast talent would actually have meaning.