Everyone on that list can sing/has talent in some capacity. Britney's exclusion makes perfect sense. She was never a musician. Just a product.
The top 5 is perfect, the order is subjective guys. These 5 women have done so much for music and depending on your taste, you could mix and match however you saw fit. Personally, I think they put Bey at 4 and not 5 or 3 just to match her favorite number. TV producers can be humorous too you know.