For me, overall, I prefer the 24-105L for portrait work, but for more general purpose work, the 24-70L II is probably the better lens, over all.
Not sure whether to be frustrated or grateful after reading this. I'm getting the 24-70 II, and had planned to sell my 24-105 this week. But you've got a great point - the flexibility to go from wide to a headshot is very useful. I'd not use it outdoors (where I prefer fast primes to blur the background), but rather indoors with a backdrop and monolight+Speedlites in softboxes. In that situation, I'm stopped down a bit because I've got plenty of light and no need for background blur, and as you say, perfect sharpness isn't usually necessary or even desirable.
If nothing else, I suppose I should hang onto the 24-105 for a while.
(By the way, I'm grateful - thanks!)
I would have kept my 24-105 if I had not needed funding for the new lens. Actually I did a lot of upgrades last fall.