Hi Michael ,
in answer to your question , i don't believe Diane Arbus really cared about the "fine print" , the way we do now. In a sense Arbus work lives by the same principles of Cartier-Bresson work .
He didn't care about printing , he hated the darkroom work , his genius was in the picture taking stage , his compositions were what drew me to photography , he opened up a door in a different reality .
Arbus work wasn't that immediate, the only fact that she was taking portrait of people aware of the picture taking stays to testify it .
I don't think she ever said she was a fine art photographer as so many of us do nowadays , she was a photographer who had developed ,if you will, her own style , and she had made it work at her own advantage.
I believe the few things she cared in her prints about was the "muddy" quality characteristic of her images.
I will also dare to say that she would use a flash to avoid dodging and burning in printing .
You see Michael, in these 20 or so years of photography , i have learned that there is no right approach in the creative field , if you develop your own tools to give voice fully to your creativity , you have done your job , and you can consider yourself an honest artist , and i believe Arbus did that fully .

"So is lack of expertise, an asset in her case. If so what does that say about you and the rest of us, trying to attain the expertise to be a great printer."

What does it say? I am not really concerned with that , in the sense that each individual makes his or her own choices in their lives.
If you make a " fine print " of an Arbus image , with zonal evaluations , contrast control , double bath development , and all that beautiful legacy that Weston, White and Adams have left us , you are inevitably bound to kill the raw power of that picture.
There is no fixed rule , i don't see anything lacking in Arbus work , her images stand by themselves, and if she didn't have great skills in the darkroom , i will not put her in the basement , just because she has chosen an unpopular way .