Actually, the ranks work. At first, I thought they hadn't been implemented yet. You just need to do a lot more to get promoted. Once your soldier's "mind" (which I consider overall skill, experience) stat reaches 50, he/she gets promoted to Lance-Corporal. 55 Corporal, 60 Sergeant, 65 Warrant Officer (I have 3), 70 Senior Warrant Officer (just got my first one).
Rank is assigned not purely based on kills, but rather "mind". Indeed, a leader must have the brain to lead; racking up kills is not necessarily a sole indicator of leadership ability. An agent gets one point of "mind" per mission, leading to a slow but sure accumulation of experience. Which agent gets a kill/kills in a mission is largely up to chance, but the agents with growing combat experience over time are likely the ones best suited to leadership.
It does take a long time to reach those first ranks, but keep sending your vets out on missions, and they'll get promoted. It's better than having an agent go on three missions in one day and reaching sergeant, as was possible in the XCOM games.
The rank insignia are a bit foreign to me (I'm in Canada), but that's fine - they seem European-inspired, and that's fine.
