In my opinion, the battle is not "3D DOF good but slow" and "Post DOF is fast but bad".
The question is to have the possibility to change it in post!
for example, we create a nice shot with 3D DOF. In preview, low res, low quality your clients say: good, I like it.
But, when you render in 4K, with good quality, they can say... O god.. It's too much, or... it's too less!
In a lot of shot, DOF 3D can be very fast (no strong highlights, no DOF reflection or reflaction), I agree.
But, in this situation, also the 2D DOF does a good job, and I can change it easily with ZDepth. =)
