How do you use barrelmancy against foes with Misty Step?
If you mean going down invisible, dumping a load of barrels and blowing them to kingdom come *before you even initiate dialogue*, that's too cheesy for me to contemplate!
Positioning your party and placing barrels/crates tactically before initiating a combat feels acceptable. It's a precaution every good adventurer would take. You can always opt not to pull the trigger. Wiping out the opposition before they can even act (and before you technically know they are enemies) seems like an exploit.
I love that the option is there for those who want it. But I'll be finding another way. I hope.