No flips for you!
Sure, you can make that argument, but then you're open to actually looking at how black powder would work. That cauldron would have been a decent bomb, but not blow the wall sky high. The culvert would have channeled most of the blast out the sides, not upwards. Explosives and solid stone don't mix well, which is why mining, even with high explosives, is more about networking smaller blasts to fracture the rock face, not blow it out. As black powder, the scene presented doesn't make much sense. As magical boom powder, it does.I have to disagree with you there - not saying that I am "right" and you are "wrong", but if you look, thematically, Saruman was a representation of technology and destructive industrialization. It would be very appropriate that Saruman invented black powder and knew how to wield it well - so the bomb wasn't a barrel, but a strong metal container that amplified its power. The narrow tunnel also amplified the destructive power.