I find small boosts, such as a +1 to AC, really useless in games. In 19 out of 20 attacks, that one AC won't make a difference. Unless you can stack that with a whole lot of other +1s and +2s, it's not going anywhere.
Meanwhile, Great Weapon fighting is necessary to get the best out of Great Weapon Master. With the accuracy loss, you need all the damage you can get. Bless only helps so much.
If a character being downed is dangerous, that's a general weakness of the party. The problem isn't Lae'Zel, it's not having a healer. In my two paladin playthrough, they ran around with 14/15 AC happily and it never even mattered. The eventual 15/17 was an upgrade, but underwhelming.
A character, specifically /Lae'Zel/ being downed was very dangerous in my caster class playthrough. If she was down, there was no picking her up again. The enemy would target and down her before she even got a turn. That made her useless.
So, it's true that Las'Zel has no tanking ability. However, that +1 AC will mean she sucks -5% less at tanking for casters, and a whole lot more in melee parties that can heal.
The crux of the matter is that you can't just have a tank and call it a day. You need a healer and a tank, or you should go full glass canon. What dies quicker can't do damage.
