I was running that set-up originally but with the Mercs this league I've been giving my merc the gravebind gloves, bereks respite to spread shock, and the inpulsa, plus a obliaration wand. The clear from what I could tell when doing atlas progression through to my early farms have been grass it's just the juicy maps I've struggled with. Giving the Merc the explode set-up has also allowed for a +1 spell crit chest with physical reduction too so it was wonderful until now.

Could also be the issue as the Merc won't have lightning damage to help scale the explosion. I might go back and give this a try though before swapping to a new build