You could let the cleric use a less-optimal version of Bend Bars, Lift Gates as a custom move. On a 10+, choose 2. On a 7-9, choose 1. (The fighter's move gets to choose 3 or 2.)
So on a 7-9 in your example, he probably picks "it doesn't take a very long time." That means it does make a lot of noise, can't be fixed again, and damages something of value. (You might have to get clever with the "something of value"; maybe ask the players. At the very least, you could do damage to the cleric or give him the Weakened condition with a seized-up back.)
Regarding the barbarian's d8+d6: I haven't run one, but I'd make be all about escalation.
The d6 is higher on a hack n' slash roll? He knocks over a brazier and starts shit on fire; smashes the orc into the pillar so hard it cracks and the ceiling starts to buckle; cleaves through the goblin and gets his sword stuck in the wall.
D6 is higher on a parley? Maybe you offend an onlooker with your impudence or rude manners. Maybe you make a softer man envious and he starts to plot against you (nothing says that the GM has to introduce the complication now).
One last thought: don't think of it so much as the 7-9 result on Defy Danger. There, the GM offers you a hard bargain, ugly choice, or worse result. The barbarian shouldn't get any choice. He acts boldly and with vigor, and damn the consequences.