All* full sized rifle rounds are supersonic and cause the cavitation the 5.56 has become infamous for (e.g. bruh it goes so fast it's basically explosive! - overheard in a cafe). The terminal effects of 5.56 on flesh are severe, but not moreso than other rifle rounds. A full sized rifle round will cause more damage and can do it from much further away.

* excepting a few that are deliberately manufactured to be subsonic, because they are niche products.

IIUC many military 5.56mm rounds are designed to fragment upon impact (against the spirit if not the letter of the Geneva convention). 7.62mm rounds are (or at least used to be) designed to hold together in one piece.

The latest military 5.56 rounds are actually steel, and designed for penetration, not fragmentation. The US army is now using M855A1(Steel core, and steel penetrating tip), which replaces the M855(jacketed steel core) What you are thinking of is the 1899 Hague Convention, not the Geneva convention. Also, the USA was not a signing country. https://www.army.mil/article/41283/army_begins_shipping_impr...

A single soldier can also carry a heck of a lot more 5.56 than 7.62

Then there's the urban legend of 5.56 being chosen because injured troops are more of a liability than dead troops

If your equation is Energy=mass*velocity^2, the 3x mass difference is much more important than the 15% velocity difference. That's why a .308 has about twice the energy.

Only when dealing with body armor. It's the reason the 45 ACP and the 12 gauge slug are still powerhouses even at relatively slow velocities, when compared to modern high velocity rounds. When body armor is taken out of the equation these rounds do as much of not more than their high velocity counterparts. You can compensate for some loss of mass with velocity but not all of it.

It's similar the the differences between horsepower and torque. To paraphrase a popular meme, Horsepower is how fast you hit the wall, torque is how much of the wall you take with you.

energy takes into account both mass and velocity. you can check the relative energies (and velocities) of common rounds on wikipedia. .308/7.62 has more energy, as the projectiles generally mass more than twice as much, and go only slightly slower.