Re: Tobi was never meant to Obito
People only liked the Izuna theory because, to the fanbase's unoriginal point of view, Izuna was the only one who could stand as an "equal" to Madara, and that was the only way our minds could justify Tobi's vast knowledge of history and Jutsu. True, it would also draw more parallels between the Madara/Izuna bros and the Itachi/Sasuke bros, but at this point I don't think their circumstances or characters are comparable (outside of Sasuke being a lot like Madara).
Obito does more in terms of developing Naruto/Kakashi, which in my opinion is far more of a curveball; I expected Tobi to be an example of what Sasuke could become if he continued his path of vengeance, but Obito is basically a corrupted version of Naruto. And yes, long time fans of Tobi feel cheated that he's basically Madara's underling, a crippled kid who owes all his power to the hated "Hashirama Cell Plot no Jutsu" and some vague training sessions with Madara. In short, he doesn't stand as an equal at all.
Obito's motives may feel "cheap" in the sense that Rin's death doesn't justify his conclusions... but to be honest, the fact is that Obito, unlike anyone else, HAD access to the power to create a perfect world, and to his fragile mind it seemed like the better alternative. It's actually not unlike people who turn to suicide, except in his mind he was saving everyone, whatever the cost.
Obito arriving in Madara's base (and his escape from rocks in general) still need to be explained, but it's important to realize that we've only gotten Obito's perspective so far, and he himself doesn't know those details... if it's ever revealed that Madara had a greater hand in Obito's kidnapping/mishaps/Rin's death/etc, I'm sure we'll get another bandage explanation (Zetsu network retrieved Obito, etc).