Rick wrote:

Frankly, I have no idea if 45 degrees is better than 30 or 80, nor do I
care. An unfeathered paddle eliminates any concern of using a control hand
and twisting the wrist. I don't know whether anyone has done injury
statistics on feathered/unfeathered, but I won't go back to a feathered
paddle. The only drawback was having to relearn the screw roll so that I
didn't twist the paddle on the sweep.

Yeah, a friend of mine does a comedy riff on this topic.
He is a class 5 kayaker who has always used unfeathered.
He makes fun of kayakers who, as a group, can't settle on a feather angle.

Personally I got tendonitis from 45 degree feathering, and went back to 60.
This is really a question of personal style and anatomy.