If I were to do something with the Amazons, I would clarify that the Bana are like the Golden Age Amazons, but mortal before moving to Themyscira. The "native" Themysciran Amazons were a step above that, with Diana being the best, and when Diana won the challenge, she was given her full gifts by her Matron Goddesses (and Hermes).
Good Lord, it's like we share a brain. That's exactly how I would handle it, via Marston's concept of Amazon Training. The reason that the Themyscirans are above the Banas (and any other splinter tribes that may be out there) is that their immortality gives them the time to hone themselves to levels that mortals cannot. For instance, a number of Themyscirans would be able to fly, whereas maybe one Bana in a generation could pull it off.
(Oh yeah-- I would make flight the capstone ability of Amazon Training. Only the most advanced Amazons would be able to fly, and naturally Diana would reach that point at an unbelievably young age)