Just like in the title, at the end of the final event we were standing at the temple’s door, near the respawn, we were surrounded, then the explosion happened and all the enemy were left standing (and we died as the result, since we expected them to drop dead and had no back up plan).
Played again, was near the statue of Sigmar, again most enemies remained intact. According to my colleague, a few actually died. Anyway, it seems that the explosion is not reliable/deals way too little damage.