Blastminer's Trap currently requires creatures to walk almost exactly over its center to trigger, making it too difficult to use effectively. It also doesn't do significant enough damage compared to other spells; it appeared one shot did about the same damage as a single "tick" of the Summon Swarm spell. Since the traps also disappear when any other spell is cast Blastminer has very limited usefulness, especially for how late in the game it is unlocked.
The spell needs a significant increase to trigger radius, an increase to damage appropriate for the limitations on the spell, and to be unlocked much earlier in the story.
