The Easiest setting is pretty easy, and I’m not humblebragging. As Mysterio also mentioned, the first time a unit falls in battle, it is only injured. I only lost some of my best guys against the boss because I assumed he wouldn’t be that hard and brought them in injured. If I would have waited, I could have brought in uninjured units. Then I would have been able to regroup after he kicked my ass and I wouldn’t have abandoned my game. I probably still could have recovered as it was, but I just considered it a quick first learning game and restarted.
The game offers you plenty of units as well, so you should always have enough to field the maximum of 6 units and then reserves that can be training, improving weapons, on scavenging missions, or just convalescing.