I'm guessing the davit arms on the 46kV are just a logical up-sizing of the ones on the distribution circuit.

That's kind of what I thought too when I used to see this line. The company actually has two separate departments on different floors- one for distribution, and one for 46-138kv (and formally 345kv before METC and the ITC bought those lines). However, when these poles were built, I wouldn't be surprised if it was all one department back then.