I have always wondered what exact idea we should have on how heavy (metrically speaking) weapons, armors, shields and otherwise are in this game. Did the devs ever set up such measures for reference?

My first clue is that normal damage/defense plays very much on their implied mass (an Ironmight Plate Mail obviously could only be quite heavy, while a Dragon Scale Mail and a Divine Cloak would be very lightweight). However, while the in-game effectiveness of many of them are very clearly based on their star rank, I have trouble seeing a Wild Hunter Blade outweighing, for example, a Heavy Hatchet. And I highly doubt that the rocket hammer's pure elemental damage output is indicative of that general basis.

The fact that a few bombs including the Big Angry Bomb, Irontech Destroyer and Graviton Vortex reduce movement speed when being charged is also telling of their impactful weight.