Question about damage and ranks - I've found what new soldiers (aquanauts) often not killing enemy in one shot what usually dies of it if someone more experienced shoot them. Same for throwing grenades.
It's a variety of subtle factors you may not be noticing, plus some apophenia. Maybe your less experienced soldiers are up toward the front and more likely to get the first shot. Maybe your more experienced soldiers carry better weapons. Maybe aliens are less likely to survive a hit gradually as the game progresses--your soldiers become more experienced but also get better weapons. Maybe you get better at using the same weapons, because you the player are more experienced and know what kills them. As for grenades and other explosives, it's probably the same, but hitting a square closer to the target counts for more damage (usually 10 more).
I've actually experienced the converse: as I research better armors, my rookies seem to become more powerful in combat. It's probably just that they can hold the line better, and it's definitely not them doing more damage.