Also, are these barrels made of paper? Why do they instantly explode when exposed to the slightest hint of fire? Would a well-sealed barrel even explode without access to plenty of oxygen? What cooper made these that they completely fall apart when, e.g. struck by an arrow? Decent barrels are pretty resilient.

They might feel less ridiculous if they were much more difficult to actually ignite. Maybe give an intact barrel and very slim chance of exploding when exposed to heat? Or maybe the outside of the barrel catches and it smokes and smolders for a minute or two before it has a chance to explode. They would feel like much less of a kick in the shins to wizards if they weren't so reliable.