I want to say 3 out of my last 4 runs with AFK were first places, in the 9k-10k range. While I occasionally end the game with more than one of my tier 3 minions, usually I don't and always get to tier 6 quickly.
I will say, I think you never pick AFK if Demons are available, otherwise you end up just losing to big wrath weavers at a time when you are supposed to be winning matches.
If your initial setup of tier 3 minions is strong you use that to transition into a real comp. I definitely have won enough of the time with AFK that I wouldn't put her in the tier of heroes that gets top 4 but never gets first place. Having said that, no I don't think she is a strong hero either. You need very specific tribes to be available before even considering her as an option, and you can get bad luck and not get the good minions even in that case.