You just don't get the intention of the mode. It is definitely not meant just to give each other the top 10 worst champions. It's supposed to force people to play outside their comfort zones.
You're under the false impression that an Annie main will be able to play EVERY OTHER MAGE AND SUPPORT exactly as well as Annie, which isn't the case.
Other examples of champions someone might main that would also leave them open to getting picks who play completely differently: Lee Sin, who is a fighter or assassin. You pick that and the enemy might give you Master Yi, who plays and builds completely differently. Or any of the juggernauts, who are considered a subtype of Fighter.
You're misunderstanding the concept as well as the "fun" of the game mode, which is part of the reason they saw so little play of Nemesis Draft and why it hasn't been seen in the rotating featured mode list.