You only need one level 100 pokemon with max happiness and your OT to get the mega bracelet. You could just catch a T1 pokemon like Magikarp or Pidgey and train it, which takes some effort but its a quest in an MMO, so I dont see any problem about that. Maybe you even have a Synchronize Alakazam ready to get the mega bracelet.
You dont need OT pokemon for most of the mega quests and for the mega starter quest everybody has to train a new catch anyway. Thats just how the quest works.