The problem with it working on a wing joint is the depth of the wing joint. The heat from a heatgun will only go so deep. And as stated, you need to keep the melted area soft with heat, so you can't stop heating one side and go over to the other cool side. The heated side cools as you heat up the other side. And you can't pry the joint apart as one side of it melts because the cool epoxy holds that wide joint closed from the other side.

Heat does soften epoxy. But it won't work on every epoxy joint. It depends on the joint size and the heating tool.

And it depends on the epoxy. I once had to use a torch because a plumber's soldering iron (them puppies are HUGE and HOT) couldn't melt it.