My main reason why Tobi isn't Obito. Since Obito and Kakashi had both 13 years when Obito "died". Now that would make Obito 14 years old because Tobi fought Minato 1 year after Obito died because Kakashi is 29-30 years old and Naruto is 16, the fight took place 16 years ago so 30-16 = 14. Kakashi was 14 when the fight took place thus Tobi can not be Obito.