I dislike Byrne's "explanation," because it doesn't fit the way Di & Artie previously interacted. Byrne has Di weaken in Artie's presence, which is wholly inconsistent with their previous scenes together.
(Though I disliked that Artie was such a stooge when she was Wonder Woman. That I could change.)
But yeah, William Messner-Loebs, sloppy writer. But Byrne's answer doesn't quite work for me.
As for Amazon powers attenuating over generations: Marston had Amazon powers as "mind over matter," deriving from craft rather than genes. I would tend toward this approach if I were writing it. Ergo, the lesser powers of the Banas should be due to technological & cultural deficits rather than "thin blood."