I think Obito being Tobi makes perfect sense. For one you have to keep in mind that the logic in Naruto functions primarily on things happening because certain characters are connected. This logic, unlike other series like Bleach and One Piece which have connections that make sense, Naruto has these extravagant explanations mixed with retcon and straight up terrible writing for how things in the world are connected. The hints of it being Obito were pretty setup and have always been even though it was very subtle.
1. His hairstyle is similar.
2. Has only one eye (pre-Rinnegan), which only a very few Naruto characters fall under that are either presumably deceased or gone.
3. Obito has a previous backstory, so essentially we've already gotten a part of Tobi's backstory shown in the series, which is already a recurring theme with major characters in the series such as Orochimaru, Narutu, Sasuke, Kakashi, Jiraiya, and even Madara. This allows Kishimoto some leeway without having to completely invent another character.
4. Tobi being someone completely uninvolved in the central character's storylines would be rather anti-climatic and boring. Kishimoto is all about doing stuff to get an emotional response from readers, which Tobi being Obito will end up doing in the long run. No one would care if Tobi was Sasuke's dad or Madara's brother, but him being Obito would cause readers to get interested as Obito is connected to a previous storyline that hasn't been touched upon in a while.
5. All potential candidates such as Madara's brother, Sasuke's dad are all legitimately dead. Obito has the possibility of being alive since we never truly see him die nor would he die of old age much like Madara himself or Madara's brother.
6. This doesn't mean much, but I remember seeing a flashback where Tobi looked rather young and shorter, which implies that he isn't some type of immortal being that has been living a long time, but rather he's just some teenager pretending to be Madara.
