Flashbangs disable almost every trick organic enemies throw at you, period. Sectoids, Codex, Stun Lancers, Vipers, flashbang'em and they are less deadly then your average trooper.
Are you using grenades to you full advantage? Grenades are awesome. They shred armor, they remove cover, they knock holes in buildings, and they detonate cars. They are so nice there is an entire class dedicated to them.
Have you considered using the Black market? You have quite a lot of Intel, Alloys, and Elerium that you could use to get a hell of a lot more supplies. If you contact the East US, you get Under The Table and bump up your profits.
Are you training your rookies? It might be a good way of at least providing more. Remember that you can get two good fighters per month in exchange for supplies and Intel at the Resistance HQ and Black Market respectively. Good for those profitable but deadly missions, and plugs the holes in your rosters.
Also don't even consider sneaking past any mission except one where you must extract to win (Alien Facilities, Hostages, etc). Since you need to kill everything eventually, use concealment to just effectively erase a pod from the map.
Believe me, my squaddies don't get guaranteed hits. Maybe just think more about elevation bonus and flanking? I don't really know what your problem is with that.