The trem block has one primary job: to be heavy. It's there to ensure that NO string vibration is transferred from the strings to the bridge, because you want all the string vibration to stay IN THE STRINGS.
Ever played a pick-up basketball game where the backboard is loosely attached to some shitty old wobbly pole, and when you take a shot the ball hits the backboard and just stops dead and falls to the ground? Or, even worse, the pole actually wobbles at a specific frequency and thus sometimes if the ball hits the backboard at just the right moment the wobbling backboard whacks the ball back up court like a tennis racquet? Those problems are removed if you attach the backboard firmly to the pole(s) on which it is mounted, and fix the poles firmly to the wall or the ground. You want all the energy to stay in the elasticity of the ball.
Same problem with guitar. You don't want any part of a floating bridge either soaking up vibration or vibrating at a frequency you don't want. You want all the energy to stay in the elasticity of the strings. But you can't fix "the poles firmly to the wall or the ground" because there's no wall or ground to attach to - the bridge is floating in mid air. That's the whole point. The only thing you can do is make the bridge as physically massive as possible so that plain old inertia approximates having a connection to something solid. That's why trem blocks are often referred to as "inertia blocks".
Now there's limited space in the back of a guitar so the most efficient way of getting the most mass into the smallest space is to use material that is very dense. Size being equal, the heavier the trem block the better because that means less string vibration is getting lost to the bridge. It doesn't matter if the material is soft or hard, strong or brittle, it just has to be DENSE. Densities of some materials that are sold to GASsing guitarists - bigger numbers are better:
Brass: approx 8.6 grams of weight per cubic centimeter of the metal
Steel: approx 7.85 g/cm3
Zinc: approx 7.14 g/cm3
Titanium: approx 4.5 g/cm3
Granite: approx 2.6 g/cm3
Summary: snake oil.
(For the guitarist who has more money than sense - gold, approx 19.3 g/cm3)