Really? I A-ranked that one on my first try. The key to victory is using Edelweiss to cover your infantry from Selvaria's attacks. I did get half of the squad knocked out and had to call in an additional sniper to take out a couple of pesky shocktroopers, but other than that it went relatively smoothly.
There are two levels later on that do rely on T&E: in one you're attacked from two sides and have to take out two tanks. The problem here are infinite reinforcements the AI has. It doesn't even need camps to get them, they simply come from outside the map. In another you have to defend a camp for 8 turns (I think) or wipe out the enemy in this time. The problem? You can't call in reinforcements, and the AI doesn't need to capture the flag in the middle of the camp (there is simply no flag). A goddamn scout may rush past your defenses, step inside the camp, and even if he has only one HP left, it's an instant game over. So cheap it's not even funny. Thankfully, this mission is completely optional.